384 NORTH AMERICAN INDEX FOSSILS. 



ments of abdomen exposed; cercopods setigerous, longer than 

 telson. Devonic. 



26. M. oceani Hall and Clarke. (Fig. 1689.) Devonic. 



Large ; lateral carina very strong, its upper surface ornamented 

 by oblique crenulations ; cercopods slightly longer than telson ; sur- 

 face of part of abdomen ridged and tubercled. 



Portage shales of New York. 



XIV. DiPTEROCARTS Clarke. 

 Carapace chitinous, in one piece; with short, narrow, anterior 

 or rostral, and broad triangular posterior notch, shorter than the 

 anterior one; sides of shield sloping. Siluric-Devonic. 



2^. D. procne Clarke. Devonic. 



Cephalic cleft very broad and short, extending one fourth the 

 length of the shield; abdominal cleft narrower and longer; line 

 of connection less than one third length of carapace ; surface con- 

 centrically striate. 



Portage and Chemung of New York. 



Order SCHIZOPODA Latreille. 



Small, elongate, aquatic forms, superficially resembling macru- 

 rous decapods ; they have compound eyes borne on movable stalks, a 

 large delicate carapace more or less completely covering the thorax, 

 and eight pairs of thoracic legs similarly formed and consisting of 

 a protopodite, with an exopodite used for swimming purposes, and 

 an endopodite. Five of the abdominal feet or pleopoda are 

 biramous swimming feet, the sixth or posterior pair forms with 

 the telson a caudal fin. The genera given below are of doubtful 

 affinities and are placed here tentatively. 



XV. PalzEOPal^mon Whitfield. 

 Shrimp-like Crustacea with a narrow carpace covering the tho- 

 racic region, not rostrated in front, but keeled on back and sides ; 

 abdomen of six smooth segments terminating in an elongate trian- 

 gular telson flanked by caudal flaps composed of five elements, of 

 which the outer four are fused into a triangular plate; legs elon- 

 gate, smooth, almost thread-like except the upper second joint. 



