On the PalcEOZoic Bivalve Entomostkaca of Canada. By T. R. 

 Jones, Esq., F.G.S. 



I. Betrichia Logani, Jones. 

 Plate XL Figs. 1-5. 



(Annals of Natural History, 3d series, vol. i. p. 244, plate ix. figs. 6-10.) 



Length. r\, breadth -J^ inch. 



This is a small BeyricMa of the unisulcate group (" Simplices," 

 Annals Nat. Hist., 2 ser. vol. xvi. p. 85) ; variable in shape, from 

 reniform to oblong ; dorsal edge straight, extremities rounded and 

 almost equal ; ventral edge varying in its convexity. Surface of the 

 valves somewhat depressed, most convex a little above the median 

 line, sloping more gently to the ventral than to the dorsal margin ; 

 usually punctate, sometimes smooth ; always bearing a distinct nar- 

 row depression on the dorsal region, usually on its anterior third ; 

 this dorsal notch reaches across a third or even more of the breadth 

 of each valve. Ventral and terminal margins bordered by a narrow 

 depressed rim. 



I cannot regard the extreme shapes of the gregarious and innume- 

 rable individuals of this Beyrichia as typical of specific distinction. 

 The general form, the relative convexity, and the dorsal notch are 

 the more characteristic features. 



a. Var. reniformis. The extreme of the kidney-shaped form is well 

 shown in fig. 1, a specimen from Hawkesbury, where this shape 

 occurs, with many of oblong outline, and others of intermediate shapes. 

 The specimen here figured is strongly punctate : smooth specimens 

 of this Variety occur at Grenville. 



h. Var. leperditioides. In fig. 5 we have one of the specimens in 



which the antero and postero-dorsal corners of the valves become 



modified towards the well-marked oblique dorsal angles of Lejjerditia.f 



Locality and Formation. — Grenville and Hawkesbury; with the 



following species in the lower part of the Chazy. 



Collector. — Sir W. E. Losfan. 



t See p. 92 for further remarks on B. Logani and its varieties, in relation to L. 

 Canadensis. 



