OF SOUTHERN INDIA. 153 



Returning again to the cretaceous species, their determination also is to a very 

 great extent very unsatisfactory, though we abeady meet here with many character- 

 istic forms. We do not find as yet true Venus, hut we meet with Mercenaria, a 

 group less numerous in the present seas than others ; some forms indicate Chione, hut 

 scarcely any resemhle Cryptogramma. Species of the genus Cytherea are by far 

 more numerous than those of Venus. "We meet some, though very few, which are 

 almost identical with recent forms of Callisfa, others very much resemhliug Cytherea 

 proper, very few somewhat allied to T'wela, but most of the species appear to 

 belong to Caryatis, which has a very wide geographical distribution, as already 

 stated. All these forms are especially prominently represented in the deposits of 

 the old continent, while in America we see that most of the species have been 

 referred to the present almost exclusively American Dione, though, as the sub-genus 

 has been restricted at the present, few belong to it, CalUsta and Caryatis besides 

 being apparently the most common. I mention this fact merely because it is an 

 additional proof of what I have already several times observed, that the present 

 geographical distribution of Molluscs was to some extent indicated already during 

 the cretaceous period. Such passing observations look very insigniflcaut by them- 

 selves, but they are solid materials, out of which the palace for geological science 

 must be built ! As regards tertiary deposits I have little to say ; the species 

 gradually become very similar to the recent ones, and so is also then* geographical 

 distribution. Caryatis during the eocene epoch is still most numerous, but then it 

 immediately passes (though scarcely in a larger number) into the present tropical 

 fauna, for we do not find it in the miocene (of Europe and America) in any number 

 nearly approximate to what occurs in the two last named epochs. 



The classification of the recent venerinm noted above will be a great help in 

 obtaining an idea of the character of the cretaceous species, of which I shall give 

 a list at the end of the general remarks on the family. 



c. Siil-family,—&VNETTINjE. 



The animal of the single recent genus referable to this sub-family is not yet 

 known, but I hope to be able before long to be in possession of one or two 

 of our common Indian species. The shell is ovately elongated, moderately com- 

 pressed, hinge with three or fom* compressed cardinal teeth and one long lunular 

 in each valve ; the posterior margin behind the beaks is peculiarly flexured, and 

 bent inside, forming a deep cavity, sometimes with corrugated sides and containing 

 the ligament hidden, or almost hidden ; the lunula is linear ; pallial sinus distinct. 



The general, in many respects Tellinoid, character of these shells appears to 

 make it probable that the animals will be somewhat distinct from those of the 

 true VFNESiN^. Deshayes suggested, as already referred to, that Snnetta may 

 belong to the Donacwm, but the form and arrangement of the hinge-teeth is 

 evidently that of the Veneridjs, and that author himself classes the allied 

 Grateloiqna in the present family. The posterior -areal excavation of the 

 suNETTiNJi is very characteristic for the recent as well as for the fossil species. 



2 p 



