340 Mr. T. R. Jones on North American 



XXX. — On some additional Palceozoic Bivaloed Entumostraca 

 from Canada. By T. Rupert Jones, F.G.S. 



To the Editors of the Annals of Natural History. 



Gentlemen, 



Within the last week, Mr. E. Bilhngs, Palaeontologist of the 

 Geological Survey of Canada, has, at Sir W. E. Logan's request, 

 submitted for my examination a series of Silurian bivalve Ento- 

 mostraca from Canada, which comprise far better individuals 

 than any that I had previously seen. 



This collection includes specimens of Leperditia from two 

 localities ; namely, 1. The east side of St. Joseph's Island, Lake 

 Huron ; and, 2. East Point, Anticosti. 



No. 1. A small specimen of grey Trenton limestone, contain- 

 ing a Bryozoon, and weathering yellowish, bears a right valve, 

 lij inch long, and \^ inch broad ; and there is a separate perfect 

 carapace of the same form (^i inch thick) from the same lime- 

 stone. The valves are of a light-brown colour ; the eye-spots 

 are indistinct ; the radiate markings of the muscle-spot are more 

 visible on the left than on the right valve; the overlapping 

 ventral edge is neither straight, nor symmetrically curved; the 

 general form of the lower half of the carapace is rounded and 

 bulky. 



No. 2. A piece of light-grey limestone (of the Upper Hudson 

 River group) bears on its weathered surface Encrinital ossicles 

 and eleven separate valves of a Leperditia of different sizes ; and 

 there is a separate perfect carapace of the same form (half an 

 inch long, ^^ inch broad, ^^^ inch thick). These specimens have 

 a rather short hinge-line, a well-marked ocular tubercle, and a 

 muscle-spot visible only by its slightly darker tint. In some 

 instances these valves appear to have a peculiar delicacy of make 

 and substance ; they slope rapidly from the central convexity ; 

 the ends of the carapace are thin ; and the overlapping part of the 

 right valve is distinctly central and neatly curved. This form 

 (No. 2) differs from that of No. 1 in having a shorter hinge-line and 

 a more prominent eye-spot ; in the apparent absence of external 

 radii to the muscle-spot; in the somewhat more delicate sub- 

 stance of the valves ; in the less thickness of the carapace, in its 

 attenuated edges before and behind, and in the symmetrical 

 curvature of the overlapping ventral edge. 



The St. Joseph's form more nearly resembles the large variety 

 of Leperditia Canadeiisis (PI. IX. figs. 16 & 17) than do the 

 Anticosti specimens ; and, as I did not feel authorized to sepa- 

 rate specifically the little Grenville varieties, that from Louck's 

 Mill, and that of Allumette, neither can I regard, at present, these 



