A Nezo Lower Caiiibriaii Fauna. — Bujt. 49 
■:^.■;;./J:.-■,.^.■v«■■/^i;^^ll^■i■s■■;>.li■■■.■i^i^.■.'.■.;■:■^::■^■.-:■ 
Fig. 2. Form of Doubtful Nature. -(Natural size.) 
It will be seen from the above synopsis that this locality 
is particularly rich in trilobite remains. In this respect it dif- 
fers in a marked degree from the two Lower Cambrian local- 
ities hitherto recognized in this region. The limestones of 
Nahant have, thus far, yielded no trilobite remains whatever, 
while at Attleboro trilobites are of subordinate importance. 
At both these localities pteropods predominate, while the 
fauna described in this paper includes but two individuals of 
this class. It is true, however, as stated above, that lime- 
stones, included in the North Weymouth series, bear pteropod- 
like fragments, which resemble those of Nahant, and may 
possibly belong to the same horizon. A fragment recently 
found by Mr. T. G. Watson on the shore near the Nahant lime- 
stone cliffs proved to contain a trilobite head of the,Agraulus 
(Strenuella) type. This suggests that the Nahant limestones 
also may be associated with trilobite bearing beds. 
It is unfortunate, in this connection, that the structural re- 
lations at North Weymouth are somewhat obscure. Profes- 
sor W. O. Crosby has recently completed a survey of this 
region. He has, very kindly, allowed me to read his manu- 
script and to refer to his conclusions. He recognizes that the 
rocks near the southern border of the North Weymouth series 
become darker in colour and less calcareous, and regards this 
as evidence of a transition in that direction toward the grey 
non-calcareous slates of Middle Cambrian age which outcrop 
just across the cove. He finds evidence of a similar change 
northward, the slates losing the red colour and becoming non- 
calcareous. From this fact, and from the occurrence of frag- 
ments of gray slate in the drift, he concludes that the red 
slates are probably bordered on the north by slates of Middle 
Cambrian age. This suggests that the North Weymouth 
slates occupy the axis of an anticline, and this is regarded 
