88 
BULLETIN OF THE LABORATORIES 
GENUS MERISTELLA, Hall. 
XIL Meristella umbonata, Billings (sp.). 
{Plate XIII, Figs. 2 a, hi) 
Shell elongate ovate, the sides forming a continuous curve from the 
umbo of the ventral valve to the front margin, with the exception of a 
very slight inward curve at the hinge extremities, not at all resembling 
those of the Ohio forms of M. cylindrica ; front margin rounded. 
Dorsal valve convex, greatest elevation at one third the distance 
from the beak, thence obtusely rounded towards the beak which is con- 
cealed by that of the ventral valve. 
Ventral valve strongly convex, forming a continuous curve from the 
anterior margin to the beak, which is spirally incurved upon the beak 
of the dorsal valve, which it more or less conceals. The ventral 
valve considerably elevated above the beak of the dorsal, more so than 
would be indicated by the figures accompanying this description. 
' Surface smooth, the concentric striae indistinct. 
Length of dorsal valve, 14 mm.; of ventral valve in the same 
specimen, 17 mm.; breadth, 14 mm.; convexity, 12 mm. Length of 
dorsal valve in a small specimen, 10 mm.; ventral valve, 12 mm.; 
breadth, 8 mm.; convexity, 8 mm. 
The first inclination was to place these specimens under Meristella 
cylindrica, but several reasons will not permit this : the size of the 
specimens is smaller, the elevation of the ventral valve is greater, the 
length of the shell is relatively smaller as compared with its . breadth, 
and considered as young of M. cylindrica, their convexity is too great. 
On the other hand they are of the same size and outline as M. iiniho- 
nata. Associated with the ordinary forms are also separated valves, 
broadly ovate in outline and more nearly resembling those forms 
described by Billings under the specific term Prinstana. Since the 
writer is of the opinion that this species is only another form of M. 
unibonata, its apparent occurrence in the same strata in Ohio with the 
form just described, seems to him an additional proof of its identity. 
Locality and position. Soldiers’ Home Quarry, Clinton Limestone. 
Specimens from this locality were kindly loaned by Mr. George Cas- 
well, of Dayton. 
