572 Contributions to Invertebrate Palaeontology. 



ENTOMOSTRICA. 

 Genus ARISTOZOE Barrande. 



Aristozoe Canadensis n. sp. 



Plate XII, figs. 17 and 18. 



Carapace of large size, being more than one and a half inches in extreme 

 length, and nearly one inch in height. Form subovate, widest at the anterior 

 end and straightened on the dorsal margin. Hinge-line straight, nearly five- 

 sixths of the entire length of the valve, and reaching nearer to the anterior 

 than to the posterior extremity. Valves very ventricose, but more especially 

 so anterior to th.e middle. Margin strong and rounded, separated from the 

 body of the valve by a distinct furrow, border narrow in front and along the 

 base, but rapidly widening at the posterior end, and again narrowed toward 

 the posterior extremity of the hinge. Anterior (ocular ?) tubercle large, more 

 than one-fourth of an inch in diameter, ovate in form, and narrowest in front, 

 situated close in the antero-cardinal angle ; its surface smooth, but capped by 

 a smaller sub-central, nipple-like tubercle. Behind the tubercle, and nearly 

 two-fifths of the length from the anterior end, there is a sharp vertical con- 

 striction of the surface, which extends from the hinge to about one-half the 

 width of the valve, where it becomes obsolete. Posterior to this there are two 

 other slight sulci, the anterior of which appears to be slightly curved. Surface 

 of the crust, so far as can be ascertained from the specimen, smooth, except 

 near the lower margin, where it is covered with distant, rounded tubercles of 

 about a twentieth of an inch in diameter each, arranged in three horizontal 

 rows, which decrease rapidly in length from below upward ; the upper one 

 containing not more than one-half as many tubercles as the lower or marginal 

 line. 



Forrtiation and Locality. — The specimen is an internal cast, in a 

 rather coarse, slightly ferrugineous sandstone. It is said to have 

 come from the Trenton formation in the Ottawa basin of Canada, 

 the exact locality unknown. I introduced it here for comparison 

 with the species of Echinocaris, under the impression that it had 

 been described by the late Mr. Billings, of the Canadian survey ; 

 but the strictest search has failed to reveal any such description, 

 and I have been obliged to give it a name, notwithstanding the un- 

 certainty of its origin. 



