292 CEETACEOUS PELECTPODA 



The shells are oblong, posteriorly usually somewhat produced, mostly concen- 

 trically striated or sulcated, covered with an epidermis ; hinge with a few cardinal 

 teeth, and a cartilage pit in both valves ; lateral teeth, if present, slightly deve- 

 loped, elongated ; pallial line entire. 



There are only a few genera referable to this family, as Fronoe, Ptychomya, 

 Anthonya, and Crassatella, of which only the last is found living. I have examined 

 the animal of Cr. radiata, Ghem., which I dredged in 2-4 fathoms near the island 

 Penang, and in the Singapore harbour. Its anatomy agrees with that of 0. pulchra 

 given in Woodward's Manual. The similarity between it and Astarte is very 

 great, but there is no special posterior anal opening in Crassatella ; the rectum 

 curves from above behind the posterior adductor, and the anus terminates freely 

 into the open space, but the attachment of the two mantle margins in that place 

 is very slight indeed and considerably stronger where their separation begins, which 

 corresponds to the anal commissure in Astarte. Considering this distinction in the 

 organisation of the animal, and the important character of the presence of an 

 internal cartilage in the shell, I believe that there is sufficient reason to retain 

 Gray's classij3.cation of Crassatetta in a special family. H. and A. Adams place 

 the genus in the Astautidje, 



The former view is also supported by the geological history of the group. We 

 see comparatively only few species of Crassathllibm represented in the mesozoic 

 strata. The greatest variety of forms seem to have existed during the cretaceous 

 period, their number increasing in the later part of that period rather rapidly, 

 and being probably here the largest. It nearly reaches that of recent species 

 during the eocene formation. The American cretaceous and tertiary deposits seem 

 to be richer than those of Europe and of the East. In the miocene time the num- 

 ber of species known is as yet small ; but to obtain an idea of the fauna of that 

 period, we must await the results of the examination of the corresponding deposits 

 in tropical countries. Of living species there are about thirty-six on record, all 

 from sub-tropical and tropical seas. 



1. JPronoe, Ag., 1843, (Act. Soc. Helvet. Lausanne, p. 304). Shell sub- 

 trigonal, like an Astarte or Cytherea, with slight concentric striation on the surface ; 

 hinge of right valve with two cardinal teeth, the anterior one extending somewhat 

 below and forming the margin of an elongated pit, above which there is a small 

 sub-lunular tooth ; a small oblique cartilage pit is situated just behind the beak and 

 a large remote posterior lateral tooth is also present ; fulcrum strongly thickened 

 (vide Quenstedt, Jura, p. 319, pi. 44, fig. 1). The hinge of the left valve must 

 possess two cardinal and one sub-lunular and one posterior double lateral tooth. 

 Type, Venulites triangularis, Schloth., fCytherea idem, apud Goldfuss), a liasic 

 species. If Quenstedt' s figure and description of the hinge of this species is 

 correct, this would be the oldest form of Cbassatellid^, though, as that author 

 remarks, the hinge-teeth of the right valve very much resemble those of a Cyprina ; 

 and should it be proved that the small pit is only an accidental depression in which 

 a part of the external ligament is situated, the generic name would have to be 



