INVERTEBRATES. 511 



MOLLUSCA. 



LAMELLIBRANCHIATA. 



Genus AVICTTLOPECTE^, McCoy. 



Avicltlopecten Unionensis, Worthen. 



PI. 28, Fig. S. 



Shell of medium size, broadly subovate in outline exclusive of the 

 ears, left valve moderately convex and oblique, anterior and postero- 

 basal margins rounded, the latter roundiug up to meet the obliquely 

 sloping edge of the posterior margin. Anterior ear rather small, tri- 

 angular, flat; posterior ear about three times as large as the anterior, 

 and more acutely angular, beak depressed, scarcely reaching beyond 

 the cardinal margin and placed considerably in advance of the middle 

 of the hinge; surface ornamented with numerous simple linear costse, 

 of which about twelve may be counted on the lower margin in the space 

 of half an inch, alternating somewhat in size, the smaller ones dying 

 out towards the umbo. Crossing these linear costae are distinct lines of 

 growth. Eight valve unknown. Length of hinge line 1.20 inch ; great- 

 est length from the umbo to the basal margin 2.25 inches, greatest 

 transverse breadth 2.10 inches. 



Position and locality : Union county, Illinois; in a dark fetid limestone, 

 probably representing the Corniferous beds of the Devonian. 



CEPHALOPODA. 



Genus PHRAGMOCERAS. 

 Pheagmocebas Walshii, M. and W. 



PI. 28, Tig. 2a,b. 

 Phragmocercu Walshii, Meek and Woiitheh, 18G6. Proceed. Acad. Nat. Sci., Philad., p. 257. 



Shell attaining a large size, clavato sublunate, being moderately 

 arched, increasing rather rapidly in size (particularly in the dorso- 



