CHONDRODONTA, A NEW GENUS OF OSTREIFORM MOL- 
LUSKS FROM THE CRETACEOUS, WITH DESCRIPTIONS 
OF THE GENOTYPE AND A NEW SPECIES. 
By Timothy W. Stanton, Ph. D. . 
Paleontologist, U. S. Geological Survey. 
A peculiar group of fossils that has hitherto been referred to the 
genus OHtrea has for some years been known to occur in the Creta- 
ceous of southern Europe and of Texas. Attention was first promi- 
nently called to it by Choffat's description and figures of Ostrea 
joanncB from Portugal. The very similar form from Texas has been 
described by Hill as 0. munsoni^ and almost simultaneously by Cragin 
as a part of Hippurites flahelUfer. Similar forms, to which reference 
will again be made, have been found in the Venetian Alps. 
All these fossils have the general shape of Ostrea., but are very thin 
compressed forms, with the two valves similar and almost invariably 
still attached to each other, and wi-th rather prominent dichotomous 
ribs. That this peculiar sculpture is not essential to the group, how- 
ever, is proved by the occurrence of the smooth species described in 
this paper. 
In connection with m}" general work on the invertebrates of the 
Comanche series, 1 have restudied Ostrea munsoni^ examining the 
types of Hill and Cragin, together with a larger suite of specmiens 
collected by myself near Austin and a few obtained by Messrs. Hill, 
Vaughan, Prather, and others at various points in Texas. By means 
of polished sections and by carefully cutting away the upper valve 
from a number of specimens, with the study of fragments and acci- 
dental fractures, it has been possible to determine satisfactorily most 
of the internal features of the shell and to prove that the species is not 
an Ostrea nor referable to any described genus. The new generic name 
Chondrodonta is therefore proposed with Ostrea mtmsoni Hill as the 
type. The new species described on a following page, though difi^er- 
ing greatly in external appearance, has the same hinge structure, and 
Proceedings U. S. National Museum, Vol. XXIV— No. 1257. 
301 
