~ 
LAMELLIBRANCHIATA. 553 
Vanuxemia suberecta. | 
VANUXEMIA SUBERECTA, 2. Sp. 
PLATE XXXVIII, FIGS. 20—22. 
Cypricardites rotundatus (part.) WHITFIELD, 1874. Rept. Geol. Sur. Wis., vol. iv, p. 208, pl. V. fig. 11. 
Casts of the interior subcircular, strongly convex, suberect, with strong erect and 
scarcely incurved beaks situated nearly one-fourth of the length of the shell behind 
the anterior extremity. Back (without hinge) nearly straight; flattened sulcus wide, 
distinct, yet not deep; vertical], causing a marked compression of the anterior part of 
the umbones; usually includes one or two obscure vertical ridges. Hinge plate 
strong, with several (?3 or 4) strongly oblique cardinal and three posterior lateral 
teeth in each valve. : 
There is no doubt in my mind respecting the specific distinctness of this shell 
and the smaller and much more abundant V.votundata. As I have already pointed 
out the difference, I shall not repeat them, but will refer the reader to the remarks 
on that species. The next species V. media, though very similar in its general expres- 
sion, is not I believe so closely related. The beaks are smaller and more incurved, 
and there is a decided concavity in the dorsal outline behind the beaks, while the 
anterior margin has a slight backward direction that is not seen in V’. swberecta. 
Formation and locality.—Upper Buff limestone of the Trenton formation at Beloit, Wisconsin. 
Mus. Reg. No. 8328. 
VANUXEMIA MEDIA, M. Sp. 
PLATE XXXVIII, FIGS. 23—26. 
Shell small, strongly convex, rounded, a little the highest posteriorly; anterior 
margin slightly oblique, dorsa] outline distinctly concave behind the beaks. Umbones 
of moderate size and prominence, but little compressed, beaks incurved. Hinge plate 
of moderate strength, the details of its structure not well determined. Anterior 
muscular scar rather small, and not so strongly defined as usual for the genus. Pal- 
lial line indistinct except for a short distance beneath the anterior muscle. 
This species, though smaller, seems to be intermediate in its character between 
V. suberecta Ulrich and V. hayiana Safford, sp. It is of more rounded form and has 
larger and more prominent umbones than the latter, while in these same features it 
fails to equal the fornfer. The anterior muscular scar is smaller and unusuaily 
shallow. Other differences may be noticed but those mentioned will, it is believed, 
suffice for the recognition of the species. 
Formation and locality.—Trenton limestone, Minneapolis and Cannon Falls, Minnesota. 
VANUXEMIA CRASSA, ”. Sp. 
PLATE XXXVIII, FIG. 27. 
This species, seems, on the whole, to have been much like V’. suberecta, but is 
readily distinguished by the remarkable strength of its hinge and the great internal 
