WHITE.] CRETACEOUS FOSSILS. 23 
Length, 29 millimeters; height, 18 millimeters; thicaness, both valves 
together, 14 millimeters. 
This species is evidently congeneric with the shell which, in the An. 
Rep. U.S. Geol. Sur. Terr. for 1877, p. 298, I described as Pachymya 
herseyi and also with the Cypricardia texana cf Roemer; but knowing 
nothing of the hinge of either of these forms I am not satisfied that they 
are properly referable to Pachymya. They are, however, here referred to 
that genus because of the agreement of their external characteristics 
with those of Pachymya. 
Position and locality.x—Cretaceous strata, Bell County, Texas, where 
it was collected by Mr. D. H. Walker. 
Genus THRACIA Leach. 
THRACIA MY A4FORMIS White. 
Plate 17, figs. 2a and bd. 
Thracia myeformis White, Jan., 1880, Proc. U. 8. National Museum, ‘vol. ii, p. 297. 
Shell transversely subovate in marginal outline; valves nearly equal; 
anterior end regularly rounded; wider and thicker anteriorly than pos- 
teriorly; posterior portion narrowed vertically and somewhat com- 
pressed laterally, but gaping at the extremity; basal border broadly 
convex; posterior border abruptly rounded; cardinal margin slightly 
convex; but the prominent umbones give the shell a concave appear- 
ance behind the beaks; a distinct linear depression is seen in the nat- 
ural cast, on each side of the ligament; beaks prominent, incurved, and 
directed a little forward; muscular impressions not distinctly shown in 
our examples, which are natural casts in chalky limestone, but the pal- 
lial sinus appears to have been large and subangular at its anterior end. 
Surface marked by the ordinary lines of growth, and also by more or 
less distinct irregular concentric wrinkles. 
Length, 57 millimeters; height, from base to umbo, 37 millimeters ; 
thickness, both valves together, 24 millimeters. 
This shell in general aspect, approaches T. proutt Meek & Hayden, 
from the Upper Fox Hills Group of the Upper Missouri River region ; 
but it differs in being proportionally narrower and more produced be- 
hind the beaks than that species, and in the greater prominence of the 
umbones. 
Position and locality.—Cretaceous strata of Bell County, Texas, where 
it was collected by Mr. D. H. Walker. 
GASTEROPODA. 
Genus MELAMPUS Montfort. 
MELAMPUS? ANTIQUUS Meek. 
» 
Plate 12, figs. 11 a b, c, and d. 
Melampus antiquus Meek, 1873, An. Rep. U. 8. Geol. Sur. Terr. for 1872, p. 507. 
The following is Mr. Meek’s description of this species, together with 
his remarks upon the same: 
“Shell subovate, thin; spire moderately prominent, conical, and ab- 
ruptly pointed; volutions about eight; those of the spire very short 
