CRUSTACEA. 207 



prolific in the remains of these gregarious creatures. Although examples of 

 the Estheria have not proven abundant, its crustacean nature is sustained by 

 its associations. 



Observations. Estheria pulex is noteworthy as being the oldest described 

 representative of the genus and the first found in America below the Trias. 

 In outline and surface markings it bears a striking resemblance to E. mem- 

 branacea, Pacht, from the Old Red of Caithness, while most of the species 

 occurring in younger rocks have the beak more anterior and the outline more 

 nearly sub-trigonal. It is known that none of the living species of Estheria 

 are properly marine animals, and it has been suggested in the original descrip- 

 tion of this species that its presence in the shales of the Hamilton group may 

 indicate the existence of pools of fresh or brackish water along the sea-shore 

 of that period. The unusual abundance of ostracodous species in association 

 with this Estheria furthers the probability of this supposition. 



Distribution. Hamilton group. In the soft shales, Miles' gully, Hopewell, 

 < Ontario count}-. 



SCHIZODISCUS, n. g. (J. M. C). 



SCHIZODISCUS CAPSA, U. sp. 

 PLATE XXXV, FIGS. 1-a. 



Carapace sub-circular or broadly ovate in outline ; greatest length along the 



hinge-line; greatest width just behind the beaks and slightly anterior to the 

 tenter of the shield. When the valves are fully expanded the width nearly 

 equals the length; normally, however, the valves appear to have been more 

 or less folded along the hinge, and when closed were probably in actual 

 contact with each other along the ventral margins. The majority of the 

 specimens found have the valves in contact along the hinge-line, but 

 expanded; a few show the valves to be laterally compressed. 



Surface gently and regularly convex and elevated at the beaks, which are 

 anterior, but distant from the extremity of the carapace by one-third its 



