LAMELLIBRANCHIATA. 628 



Cuheamya oblonga.] 



CUNEAMTA OBLONGA, W. Sp. 

 PLATE XXXVI, FIGS. 40-41. 



This species is very much, like C. truncatula, diflfering from it chiefly in the follow- 

 ing respects: The anterior end is more rounded, the lunule shorter and smaller, and 

 the posterior end a trifle narrower and much less oblique, being almost vertical; the 

 hinge line is longer, terminates posteriorly more abruptly and is nearly parallel with 

 the basal margin. The posterior umbonal ridge is less narrowly rounded, the mesial 

 sulcus about the same or slightly deeper, while the part of the shell in front of this 

 sulcus, is practically without the anterior sulcus which is such a characteristic 

 feature of C. truncatula and C. coriformis. This sulcus however is indicated by a slight 

 flattening of the anterior slope. Finally, the surface corrugations are a grade finer. 

 C. miamiensis H. and W., is similarly marked but has a diflferent outline and much 

 less distinct mesial sulcus. In the matter of outline C. scapha H. and W., another 

 Ohio species, agrees more nearly, but in that species the lunule and escutcheon are 

 both wider and longer, and the surface markings quite different from those of C. 

 ohlonga. 



Formation and locality. — Galena limestone, Dixon, Illinois. 



Genus SPHENOLIUM, S. A. Miller. 



SphenoUum, S. A. Milleb, 1889. North Amer. Geol. and Pal. p. 513. 



Shell of medium size and larger, thin, strongly ventricose, very inequilateral, 

 elongate, occasionally with subparallel dorsal and ventral margins, but usually much 

 the highest posteriorly. Beaks incurved; umbones prominent, large and full; 

 umbonal ridge strongly rounded or subangular. No mesial depression or sulcus. 

 Lunule present, usually small and sometimes not sharply defined; escutcheon prac- 

 tically wanting. Surface concentrically lined; occasionally also with radiating 

 striae. Ligament probably both internal and external. Hinge apparently edentu- 

 lous; muscular scars very faint, not determined with certainty. 



Type: S. (Orthodesma) cuneiforme S. A. Miller. 



Too little is known of this genus to determine its aifinities with any thing like 

 certainty. So far as the known characters admit of judgment they indicate relations 

 with the Grammysiidce and the PholadeUidce. Dr. Miller places the genus near 

 Orthodesma, but in this he is undoubtedly in error. 



The two Trenton species following are perhaps, not strictly referable to Spheno- 

 Uum, being too narrow posteriorly. In all other respects, however, they agree well 

 enough with the more typical species of the Cincinnati rocks. Besides, I believe I 



