462 GEOLOGY OF OHIO. 



backward, with a bifurcation at the anterior third of its length. Surface of the 

 abdomen essentially smooth. Caudal flaps marked by impressed lines, increased in 

 number and fineness from above downwards. 



The following species is introduced for comparison with Echino- 

 caris : 



EXTOMOSTRACA. 



Genus ARISTOZOE Barrande. 



Aristozoe Canadensis n. sp. 



Plate VIII, 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 pos- 

 terior extremity. Valves very ventricose, but more especially so anterior to the 

 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 (occular?) tubercle large, more than one-fourth of an inch in 

 diameter, ovate in form, and narrowest in front, situated close in the antero-car- 

 dinal 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 ante- 

 rior end, there is a sharp vertical constriction 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. 



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

 rather coarse, slightly fermgineous 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 uncertainty of its origin . 



SPECIES FROM THE HURON SHALES. 



MOLLUSCOIDA. 



BRACHIOPODA. 



Genus UNGULA Brugiere. 



Lingula ligea. 



Plate VII. figs. 3 and 4. 



-Lingula ligea Hall, Pal., N. Y., vol. 4, pp. 7 and 8, pi. 1, fig. 2. 



Shell elongate-oval, widest in the middle, and nearly twice as long as wide, 

 very slightly pointed at the upper end and neatly rounded in front, surface of the 



