.. . , , , LAMELLIBRANOHIATA. 553 



Vanuxemla suberecta.] 



Vanuxemia stjberecta, n. sp. 



'■ PLA.TE XXXVIII, FierS.,^0-23. 



Oypricardites rotundatus (part.) WmTFiELD, 1874. Rept. Geol. Sur. Wis., vol. iv, p. 208, pi. V. flg. 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. rotundata. 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. suherecta. 



Formation and locality. — Upper Buff limestone of the Trenton formation at Beloit, Wisconsin. 

 'Mus. Reg. 'So. 8328. ' 



Vanuxemia media, n. sjp. 



PLATE XXXVIII, FIGS. 23-26. 



Shell small,, strongly convex, rounded, a little the highest posteriorly; anterior 

 margin slightly oblique, dorsal 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 determine*. Anterior 

 muscular scar rather small, and not so strongly defined as usual for the genus. JPal- 

 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. mherecta 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 former. The anterior muscular scar is smaller and unusually 

 shallow. Other differences may be noticed but those mentioned will, it is believed, 

 suffice for the recognition of the species. 



Formation and focaZi^.— Trenton limestone, Minneapolis and Cannon Falls, Minnesota. 



Vanuxemia crassa, n. sp. 



PLATE XXXVIII, FIG. 27. 



This species, seems, on the whole, to have been much like F. suherecta, but is 

 readily distinguished by the remarkable strength of its hinge and the great internal 



