LAMELLIBRANCHIATA. 623 
Cuneamya oblonga. ] 
CUNEAMYA OBLONGA, 7. Sp. 
PLATE XXXVI, FIGS. 40—41. 
This species is very much like C. truncatula, differing from it chiefly in the follow- 
ing respects: The anterior end is more rounded, the !unule 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 
suleus 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 different outline and much 
less distinct mesial suleus. In the matter of outline C. seapha 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. 
oblonga. 
Formation and locality.—Galena limestone, Dixon, Illinois. 
Genus SPHENOLIUM, S. A. Miller. 
Sphenolium, 8. A. MILLER, 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 
strie. Ligament probably both internal and external. Hinge apparently edentu- 
lous; muscular scars very faint, not determined with certainty. 
Type: 8S. (Orthodesma) cuneiforme S. A. Miller. 
Too little is known of this genus to determine its affinities with any thing like 
certainty. So far as the known characters admit of judgment they indicate relations 
with the Grammysiide and the Pholadellide. 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- 
lium, 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 
