Palieozoic Bivalved Entomosiruca. 247 



Sheik's Islaiul, Cornwall, on the St. Lawrence* ; with Atnjpa 

 plena (Chazy). 



Cornwall; in the Trenton limestonef. 

 Lancaster; in the Black River limestone J. 

 Winchester; in the Trenton limestone §. 



Beyrichia Lor/ani and Lcpcrditia Canadensis occur together in 

 luuncnse numbers, forming indeed a considerable portion of the 

 rock — a limestone, 1 foot 10 inches thick — in which they are 

 chu'lly found. I believe that the former is not the young of the 

 latter" (although, perhajis, the differences of shaj)e and structure 

 are not greater than such as we find to occur between the young 

 and adult forms of recent Entomostraca and other Crustacea), 

 because, where the allied Beyrichia, such as B.strangulata\\, B. 

 mundula, and Ji. simplex, occur, even in equal numbers, in the 

 rocks of other localities, the Leperditice are not found with them ; 

 the latter also occurring unaccompanied by these Beyric/iiie ; and 

 L. Canadensis itself being found isolated in Grande Isle. The 

 close resemblance in outline of some specimens of B. Luf/ani 

 (var. B. leperditioides, fig. 10) to the Leperditice is, I believe, 

 merely a mimetic resemblance of outline, such as we find taking 

 j)lace among many groups, both of the lower and the biglier 

 animals. 



3. Leperditia Anna^, spec. nov. PI. IX. fig. 18. 



Length ^, breadth i inch. 



Small, convex; ovate-oblong, somewhat narrower in front 

 than behind ; the ventral curve nearly uniform ; hinge-line 

 straight; dorsal angles slightly truncate. Surface of valves most 

 convex at the posterior third ; smooth, thickly punctate, each of 

 the little shallow circular pits having a minute central tubercle. 

 Eye-spot distinct and raised. 



Several valves of this neatly-pitted Leperditia are present in a 

 small hand-specimen of a hard, dark-coloured, concretionary 

 limestone, under the zone o{ Atnjpa plena, and belonging to the 

 Calcifcrous Sandrock, from "immediately behind the village of 

 St. Ann's**,'' at the contiucncc of the Ottawa and St. Lawrence. 

 This is probably the oldest known species of the genus. 



* Geol. Surv. Canada Report, 1851-52, p. 70. t Ibid. 



Xlbid. p. 71. § Il'id. p. 72. 



II Beyrichia strangulata takes on a variety of forms (see Annals Nat. 

 Hist. vol. xvi. pi. (i. tii^s. 18-22) analogous to those of B. Logani. 



IT Referred to in Quart. .lourn. Gcol. Soc. vol. viii. p. 20-1. 



** Quart. Journ. Geol. Soc. loc. cit. ; and Geol. Surv. Canada, Report, 

 1851-52, p. 16. 



