336 Description of new North American Trihbites. 



in front is almost rectilinear ; the posterior angles or horns of the 

 crescent, are very acute, and project a little on each side, beyond 

 the abdomen. The front or middle lobe of the buckler, is near- 

 ly straight before, and is marked with two short oblique grooves 

 on each side ; the anterior groove has a little pit, or depression 

 of the shell, immediately before it on each side. The cheeks are re- 

 markably large in proportion to the front, and there is a raised line 

 passing over them from the front, nearly parallel with its edge, and 

 also with that of the buckler ; this organization gives to the head a 

 quadrilateral appearance ; much more obvious in some specimens than 

 in others. The oculiferous tubercles can scarcely be discerned ; 

 in some of the fragments of the buckler which I have examined, I 

 could not discover them at all. The abdomen is composed of twelve 

 articulations ; the costal arches or ribs are marked on their upper sur- 

 face with a groove, and they terminate in free angular extremities. 

 The middle lobe of the back is scarcely tapering, till within a few 

 articulations of the extremity of the tail. The tail is quite short, 

 rounded, and without the membranaceous expansion so common 

 in the Asaphs ; indeed this species forms an inosculating link between 

 the genus Calymene and Asaphus. 



I am indebted to the kindness of Dr. J. E. Dekay for this species. 

 It occurs in a loose, bituminous shaly limestone full of iron pyrites. 

 It was found in the State of New York, probably at Newport. The 

 whole animal is very much depressed ; and the rock is completely 

 filled with its mutilated remains, some of which are still covered with 

 the original crustaceous shell. 



Paradoxides Harlani. — Green. 



The contour of the buckler in this species, cannot be satisfactorily 

 determined from our present specimen ; the anterior and posterior 

 parts of it are well defined, but the cheeks on each side are either 

 mutilated or obscured. The front is very much elevated above 

 the surface of the cheeks. It rises a little before the anterior edge of 

 the buckler ; is rounded in front, and gradually tapers towards the mid- 

 dle lobe of the abdomen, with which it forms a regular continuation. 

 On its posterior surface there are three transverse furrows ; the upper 

 one crosses it a little obliquely, and there is on each side above, a consid- 

 erable protuberance. The cheeks were no doubt in the form of spheri- 

 cal triangles, but whether the outer angles terminated in acute prolon- 

 gations, cannot from our specimen be determined. The organs of vis- 

 ion appear to be entirely wanting. There are two shallow depres- 



