LAMELLIBRANCHIATA. 561 
Vanuxemia wortheni.] 
As it reads I should say that he refers to a species of Cyrtodonta like C. glabella or 
C. persimilis and not to a Vanuxemia which the shell here under consideration 
undoubtedly is. The latter differs in at least two important respects from the 
characters brought out in Hall’s description, and either one would in my opinion, be 
sufficient to defeat specific identity. Thus, he says the beaks are “situated about 
one-fourth the length of the shell from the anterior end,” whereas in Whitfield’s 
niota they are much nearer the anterior extremity ; then he gives the impression 
that the anterior, posterior and basal margins are almost uniformly rounded, while 
in the present species, the outline is always more or less quadrangular. Under the 
circumstances I might have been justified in proposing a new name, but as the 
questions involved would still be open (a study of the original of Hall’s description 
alone can answer them), it seemed best to refer to the species provisionally as 
above. 
Vanuxemia niota Whitfield (?Hall) sp., is closely related to V. hayniana Safford 
sp., and V. gibbosa Ulrich. From the first it is distinguished by its greater convexity 
and length, more anterior and larger beaks, and almost rectangular instead of 
rounded anterior side. The cast figured on plate xxxvur preserves the impressions 
of the hinge teeth. The cardinal teeth were rather small, oblique, and numbered 
four in each valve. The posterior teeth were slender, nearly horizontal, and three 
in number. In V. gibbosa the anterior margin forms a wider angle with the hinge 
_ line, the shell was a little thicker, the hinge stronger, and the cardinal teeth larger, 
not exceeding three in number and less oblique. In artificial casts of that species 
the anterior muscular scar proved to be comparatively larger, and to project farther 
anterior to the filling of the beaks, which again are of larger size than in niota. V. 
wortheni of the Galena belongs to the same group of species but is a much larger 
and rounder shell, and in casts has more compressed and less incurved beaks. 
Formation and locality.—Top of the ‘‘ Lower Blue Beds,” and base of the ‘‘ Upper Buff Beds” of the 
Trenton formation at Beloit and Mineral Point, Wisconsin, and Rockton, Illinois. 
Mus. Reg. No. 8321, 8325. 
VANUXEMIA woRTHENI Ulrich. 
PLATE XXXIX, FIGS. 6 and 7. 
Cypricardites, sp., undet., MEEK and WORTHEN, 1868. Ill. Geol. Sur., vol. iii, p. 311. 
Cypricardites worthent ULRicH, 1888. Amer. Geol., vol. 1, p, 180. 
Shell large, moderately ventricose, suberect, subcircular, the length a little 
greater than the hight, the beaks nearly terminal, the dorsal margin almost straight, 
rather long and with the extremities rounding abruptly, the anterior one scarcely 
projecting beyond the point of the beaks; the rest of the outline rounded with the 
—36 : . 
