diff --git a/beacon_chain/beacon_node.nim b/beacon_chain/beacon_node.nim
index 1914a529c..5cdcd1c08 100644
--- a/beacon_chain/beacon_node.nim
+++ b/beacon_chain/beacon_node.nim
@@ -307,13 +307,16 @@ proc scheduleEpochActions(node: BeaconNode, epoch: uint64) =
       committeesIdx = get_shard_committees_index(nextState, slot)
 
     #for shard in node.beaconState.shard_committees_at_slots[committees_idx]:
-    for crosslink_committee in get_crosslink_committees_at_slot(node.beaconState, committees_idx):
+    for crosslink_committee in get_crosslink_committees_at_slot(
+        node.beaconState, committees_idx):
       #for i, validatorIdx in shard.committee:
-      for i, validatorIdx in crosslink_committee.a:
+      for i, validatorIdx in crosslink_committee.committee:
         let validator = node.getAttachedValidator(validatorIdx)
         if validator != nil:
           #scheduleAttestation(node, validator, slot, shard.shard, shard.committee.len, i)
-          scheduleAttestation(node, validator, slot, crosslink_committee.b, crosslink_committee.a.len, i)
+          scheduleAttestation(
+            node, validator, slot, crosslink_committee.shard,
+            crosslink_committee.committee.len, i)
 
   node.lastScheduledEpoch = epoch
   let
diff --git a/beacon_chain/fork_choice.nim b/beacon_chain/fork_choice.nim
index 2156eaba3..c2a5592c9 100644
--- a/beacon_chain/fork_choice.nim
+++ b/beacon_chain/fork_choice.nim
@@ -98,7 +98,7 @@ proc getAttestationsForBlock*(pool: AttestationPool,
   for slot in firstSlot .. lastSlot:
     let slotDequeIdx = slot.int - pool.startingSlot
     if slotDequeIdx >= pool.attestations.len: return
-    let shardAndComittees = get_shard_committees_at_slot(lastState, slot)
+    let shardAndComittees = get_crosslink_committees_at_slot(lastState, slot)
     for s in shardAndComittees:
       if pool.attestations[slotDequeIdx][s.shard].isSome:
         result.add pool.attestations[slotDequeIdx][s.shard].get
diff --git a/beacon_chain/spec/beaconstate.nim b/beacon_chain/spec/beaconstate.nim
index ed0652ef7..3e453b121 100644
--- a/beacon_chain/spec/beaconstate.nim
+++ b/beacon_chain/spec/beaconstate.nim
@@ -249,12 +249,12 @@ func get_attestation_participants*(state: BeaconState,
   let crosslink_committees = get_crosslink_committees_at_slot(state, attestation_data.slot)
 
   # TODO investigate functional library / approach to help avoid loop bugs
-  assert any(
+  assert anyIt(
     crosslink_committees,
-    func (x: tuple[a: seq[ValidatorIndex], b: uint64]): bool = x[1] == attestation_data.shard)
+    it[1] == attestation_data.shard)
   let crosslink_committee = mapIt(
-    filterIt(crosslink_committees, it.b == attestation_data.shard),
-    it.a)[0]
+    filterIt(crosslink_committees, it.shard == attestation_data.shard),
+    it.committee)[0]
   assert len(aggregation_bitfield) == (len(crosslink_committee) + 7) div 8
 
   # Find the participating attesters in the committee
diff --git a/beacon_chain/spec/datatypes.nim b/beacon_chain/spec/datatypes.nim
index 1fa16c91f..d8a5582fd 100644
--- a/beacon_chain/spec/datatypes.nim
+++ b/beacon_chain/spec/datatypes.nim
@@ -382,15 +382,6 @@ type
     shard_block_root*: Eth2Digest ##\
     ## Shard chain block root
 
-  ShardCommittee* = object
-    shard*: uint64
-    committee*: seq[ValidatorIndex] ##\
-    ## Committe participants that get to attest to blocks on this shard -
-    ## indices into BeaconState.validator_registry
-
-    total_validator_count*: uint64 ##\
-    ## Total validator count (for proofs of custody)
-
   Eth1Data* = object
     deposit_root*: Eth2Digest ##\
     ## Data being voted for
@@ -432,6 +423,9 @@ type
     DOMAIN_EXIT = 3
     DOMAIN_RANDAO = 4
 
+  # TODO: not in spec
+  CrosslinkCommittee* = tuple[committee: seq[ValidatorIndex], shard: uint64]
+
 template epoch*(slot: int|uint64): auto =
   slot div EPOCH_LENGTH
 
diff --git a/beacon_chain/spec/validator.nim b/beacon_chain/spec/validator.nim
index cfdca9cc0..79a433eea 100644
--- a/beacon_chain/spec/validator.nim
+++ b/beacon_chain/spec/validator.nim
@@ -73,7 +73,8 @@ func get_current_epoch_committee_count_per_slot(state: BeaconState): uint64 =
   )
   get_epoch_committee_count(len(current_active_validators))
 
-func get_crosslink_committees_at_slot*(state: BeaconState, slot: uint64) : seq[tuple[a: seq[ValidatorIndex], b: uint64]] =
+func get_crosslink_committees_at_slot*(state: BeaconState, slot: uint64):
+    seq[CrosslinkCommittee] =
   ## Returns the list of ``(committee, shard)`` tuples for the ``slot``.
 
   let
@@ -119,18 +120,6 @@ func get_crosslink_committees_at_slot*(state: BeaconState, slot: uint64) : seq[t
      (slot_start_shard + i.uint64) mod SHARD_COUNT
     )
 
-func get_shard_committees_at_slot*(
-    state: BeaconState, slot: uint64): seq[ShardCommittee] =
-  # TODO temporary adapter; remove when all users gone
-  # where ShardCommittee is: shard*: uint64 / committee*: seq[ValidatorIndex]
-  let index = state.get_shard_committees_index(slot)
-  #state.shard_committees_at_slots[index]
-  for crosslink_committee in get_crosslink_committees_at_slot(state, slot):
-    var sac: ShardCommittee
-    sac.shard = crosslink_committee.b
-    sac.committee = crosslink_committee.a
-    result.add sac
-
 func get_beacon_proposer_index*(state: BeaconState, slot: uint64): ValidatorIndex =
   ## From Casper RPJ mini-spec:
   ## When slot i begins, validator Vidx is expected
diff --git a/beacon_chain/state_transition.nim b/beacon_chain/state_transition.nim
index 45a051723..0f67711e2 100644
--- a/beacon_chain/state_transition.nim
+++ b/beacon_chain/state_transition.nim
@@ -535,21 +535,21 @@ func processEpoch(state: var BeaconState) =
   #      these closures outside this scope, but still..
   let statePtr = state.addr
   func attesting_validator_indices(
-      crosslink_committee: tuple[a: seq[ValidatorIndex], b: uint64], shard_block_root: Eth2Digest): seq[ValidatorIndex] =
+      crosslink_committee: CrosslinkCommittee, shard_block_root: Eth2Digest): seq[ValidatorIndex] =
     let shard_block_attestations =
       concat(current_epoch_attestations, previous_epoch_attestations).
-      filterIt(it.data.shard == crosslink_committee.b and
+      filterIt(it.data.shard == crosslink_committee.shard and
         it.data.shard_block_root == shard_block_root)
     get_attester_indices(statePtr[], shard_block_attestations)
 
-  func winning_root(crosslink_committee: tuple[a: seq[ValidatorIndex], b: uint64]): Eth2Digest =
+  func winning_root(crosslink_committee: CrosslinkCommittee): Eth2Digest =
     # * Let `winning_root(crosslink_committee)` be equal to the value of
     #   `shard_block_root` such that
     #   `sum([get_effective_balance(state, i) for i in attesting_validator_indices(crosslink_committee, shard_block_root)])`
     #   is maximized (ties broken by favoring lower `shard_block_root` values).
     let candidates =
       concat(current_epoch_attestations, previous_epoch_attestations).
-        filterIt(it.data.shard == crosslink_committee.b).
+        filterIt(it.data.shard == crosslink_committee.shard).
         mapIt(it.data.shard_block_root)
 
     # TODO not covered by spec!
@@ -568,18 +568,18 @@ func processEpoch(state: var BeaconState) =
         max_val = val
     max_hash
 
-  func attesting_validators(crosslink_committee: tuple[a: seq[ValidatorIndex], b: uint64]): seq[ValidatorIndex] =
+  func attesting_validators(crosslink_committee: CrosslinkCommittee): seq[ValidatorIndex] =
     attesting_validator_indices(crosslink_committee, winning_root(crosslink_committee))
 
-  func attesting_validator_indices(crosslink_committee: tuple[a: seq[ValidatorIndex], b: uint64]): seq[ValidatorIndex] =
+  func attesting_validator_indices(crosslink_committee: CrosslinkCommittee): seq[ValidatorIndex] =
     attesting_validator_indices(crosslink_committee, winning_root(crosslink_committee))
 
-  func total_attesting_balance(crosslink_committee: tuple[a: seq[ValidatorIndex], b: uint64]): uint64 =
+  func total_attesting_balance(crosslink_committee: CrosslinkCommittee): uint64 =
     sum_effective_balances(
       statePtr[], attesting_validator_indices(crosslink_committee))
 
-  func total_balance_sac(crosslink_committee: tuple[a: seq[ValidatorIndex], b: uint64]): uint64 =
-    sum_effective_balances(statePtr[], crosslink_committee.a)
+  func total_balance_sac(crosslink_committee: CrosslinkCommittee): uint64 =
+    sum_effective_balances(statePtr[], crosslink_committee.committee)
 
   block: # Eth1 data
     if state.slot mod ETH1_DATA_VOTING_PERIOD == 0:
@@ -714,9 +714,12 @@ func processEpoch(state: var BeaconState) =
       for crosslink_committee in crosslink_committees_at_slot:
         # TODO https://github.com/ethereum/eth2.0-specs/blob/master/specs/core/0_beacon-chain.md#crosslinks-1
         # but this is a best guess based on reasonableness of what "index" is
-        for index in crosslink_committee.a:
+        for index in crosslink_committee.committee:
           if index in attesting_validators(crosslink_committee):
-            state.validator_balances[index.int] += base_reward(state, index) * total_attesting_balance(crosslink_committee) div total_balance_sac(crosslink_committee)
+            state.validator_balances[index.int] +=
+              base_reward(state, index) *
+                 total_attesting_balance(crosslink_committee) div
+                  total_balance_sac(crosslink_committee)
           else:
             # TODO underflows?
             state.validator_balances[index] -= base_reward(state, index)
diff --git a/research/serialized_sizes.nim b/research/serialized_sizes.nim
index d1c73bd2f..154aa59b0 100644
--- a/research/serialized_sizes.nim
+++ b/research/serialized_sizes.nim
@@ -16,7 +16,7 @@ proc stateSize(deposits: int, maxContent = false) =
     let
       crosslink_committees = get_crosslink_committees_at_slot(state, 0)
       validatorsPerCommittee =
-        len(crosslink_committees[0].a) # close enough..
+        len(crosslink_committees[0].committee) # close enough..
     for a in state.latest_attestations.mitems():
       a.participation_bitfield.setLen(validatorsPerCommittee)
   echo "Validators: ", deposits, ", total: ", state.serialize().len
diff --git a/research/state_sim.nim b/research/state_sim.nim
index 9b2c80c88..59307d438 100644
--- a/research/state_sim.nim
+++ b/research/state_sim.nim
@@ -54,7 +54,7 @@ cli do(slots = 1945,
       # attesterRatio is the fraction of attesters that actually do their
       # work for every slot - we'll randimize it deterministically to give
       # some variation
-      let scass = get_shard_committees_at_slot(state, state.slot)
+      let scass = get_crosslink_committees_at_slot(state, state.slot)
 
       for scas in scass:
         var
diff --git a/tests/testutil.nim b/tests/testutil.nim
index 13c6ab72d..0617076f6 100644
--- a/tests/testutil.nim
+++ b/tests/testutil.nim
@@ -169,7 +169,7 @@ proc makeBlock*(
   addBlock(next_state, previous_block_root, body)
 
 proc find_shard_committee(
-    sacs: openArray[ShardCommittee], validator_index: ValidatorIndex): ShardCommittee =
+    sacs: openArray[CrosslinkCommittee], validator_index: ValidatorIndex): CrosslinkCommittee =
   for sac in sacs:
     if validator_index in sac.committee: return sac
   doAssert false
@@ -179,7 +179,7 @@ proc makeAttestation*(
     validator_index: ValidatorIndex, flags: UpdateFlags = {}): Attestation =
   let
     sac = find_shard_committee(
-      get_shard_committees_at_slot(state, state.slot), validator_index)
+      get_crosslink_committees_at_slot(state, state.slot), validator_index)
     validator = state.validator_registry[validator_index]
     sac_index = sac.committee.find(validator_index)