244 Mr. T. R. Jones on North American 



{From Canada.) 

 1. Beyrichia Logani^j spec. nov. PI. IX. figs. 6-10. 



Length ■^■^, breadth -^^ inch. 



This is a small Beyrichia 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. Sur- 

 face of the valves somewhat depressed, most convex a httle 

 above the median line, sloping more gently to the ventral than 

 to the dorsal margin; usually punctate, sometimes smooth; 

 always bearing a distinct narrow 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 in- 

 numerable 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. 6, a specimen from Hawkesbury, occur- 

 ring with others like it, with many of oblong outline, and 

 some of intermediate shapes. The specimen here figured is 

 strongly punctate : smooth specimens of this variety occur at 

 Grenville. 



b, Var. leper ditioides. In fig. 10 we have one of the speci- 

 mens in which the antero- and postero-dorsal corners of the 

 valves become modified towards the well-marked oblique dorsal 

 angles of Leperditia-\ . 



Localities. Grenville and Hawkesbury ; in the " two-foot lime- 

 stone,^' in the upper part of the Calciferous Sandrock (see 

 further on, p. 245). 



2. Leperditia Canadensis i, spec. nov. PI. IX. figs. 11-15. 



Length ^, breadth y^^^ inch. 



Small ; somewhat variable in shape, but always retaining the 

 characteristic Leperditia-outline, with straight back, more or 

 less obliquely-rounded belly, and sloping dorsal angles. Cara- 

 pace usually short (the height or breadth being about two-thirds 

 of the length), somewhat variable in the amount of convexity 



* Referred to in Quart. Journ. Geol. Soc. vol. viii. p. 207. 

 t See p. 24/ for further remarks on B. Logani and its varieties, in rela- 

 tion to L. Canadensis. 



X Referred to in Quart. Journ. Geol. Soc, vol. viii. p. 202 & p. 20/. 



