714 Evolution of Forms from Clinton to Niagara Group [September, 



M. intermedia ; one branch developing in width while the other 

 became narrow and elongate. 



Thus far no Meristime have been found with a pronounced 

 mesial fold, of which M. naviformis of the Clinton, and M. maria 

 of the Niagara may be considered as types, although an interme- 

 diate form will, I think, be found. 



The three specimens of Stephanocrinus gcmmiformis found, all 

 show a marked angularity of form similar to some young S. an- 

 gulatus. 



A Lcptaena occurs in this rock that seems to be intermediate 

 between L. sericea and L. transversals, which it resembles in the 

 convexity of the dorsal and the concavity of the ventral valves, 

 while in texture, which is punctate and not so strongly striate as 

 in L. transversalis, and by its wide lateral alation, it is more 

 closely allied to L. sericea. Therefore I propose the name Lep« 

 tana sericea var. intermedia, as it undoubtedly represents the stage 

 through which L. sericea passed before developing into what is 



The Atrypa nodostriata found here does not have so prominent 

 a mesial fold as the Niagara forms, it being more gradual, and 

 but little more pronounced than is found to be the case in gib- 

 bous specimens of A. reticularis from the Clinton. 



Other species show slight variations from the Niagara types, or 

 perhaps, more properly speaking, the types vary from the transi- 



Thus it will be seen that in many ways this apparently unim- 

 portant thin stratum, with its limited areas, that has been over- 

 looked by the hundreds of geologists that have traversed this far- 

 famed geological field, who probably have been lured from greater 

 palaeontological wealth by the tempting display of finely weath- 

 ered-out fossils on the shale banks immediately above, as well as 

 discouraged by the difficulty of wrenching the treasures from its 

 flint-like grasp, plays a very important factor in the connecting 



chain 



of palaeontological evolution. 



It bind< 



; togeth 



er in closer 



unity 



two for 



mations by its intern: 



lediate character, 



and also by 



the blending 



in it of forms befon 



=> considei 



ed characteristic ot 



these 



two well 



l-defined groups. 









Duci 



na solitari 



a (n. sp.).— Shell oval, veil 



tral valve wi 



th promim 



,nt apex ; slope 



convex, 



, slightly incurved near the apex on tl 



le posterior 





,jrlj niarke.M') 





d concemr 



ic lamin.v, of which, near t 







,;: l "' i;! ' l I !L !,!'l 



