136 CEETACEOUS PELECYPOBA 



DONAX, Linne, 1758. 

 DoNAX, sp. ind,, PL V, Pig. 4. 



I haye figured this form simply to draw attention to this very interesting 

 species, apparently the first occurrence of a true Donax in the eastern cretaceous 

 deposits. The form of the right valve (the only one found) entirely agrees with 

 typical Donaces, except that it is somewhat more convex than most other allied 

 forms are. The specimen is only a cast, but the impression of the cardinal, a strong 

 anterior and a small approximate posterior lateral tooth, are distinctly traceable. It 

 could be suggested that the shell was a Tellina, there being some such similar forms 

 belonging to Mcera and also to Macoma, but the very strong marginal impressions 

 of the shell clearly indicate its solid structure, such as we find to be characteristic 

 in Donax, It is to be hoped that further researches will be successful in procuring 

 better materials from which the species may be sufficiently characterized. 



Locality. — South-east of Parchairy, in a brownish calcareous sandstone. 



Formation, — Trichinopoly group. 



IV. Order. VENERACEA. 



Taking the family ViEi^TiMiBM as including the most typical forms of this order, 

 the animals are characterized by an oblong, moderately thick form with the mantle 

 margins widely open in front, and posteriorly with two separated, moderately 

 elongated, siphons; the foot is generally large, laterally compressed, sometunes 

 ( Carbiid^) rounded near the base, often with a byssa] groove, but rarely with 

 the byssus developed, pointed at the end ; there is one pair of elongated gills on 

 either side of the body, and the labial palps are large and sub-trigonal. 



The shells are oblong, generally longer than high, sometimes rounded, mostly 

 closed in front, slightly gaping posteriorly, solid and covered with a thin deciduous 

 epidermis. The hinge is composed of two or more cardinal teeth in each valve, 

 either fitting one beside the other or crossing each other ; lateral teeth are often 

 present. The muscular impressions are generally well marked, oval, slightly 

 impressed, the pallial line slightly sinuated, or entire; the ligament is always 

 external. 



The families belonging to this order are five; the Fetricolii)^, Venbuid^, 

 Glossid^, Cyrenibje, and Garbiidm. This arrangement is considerably different 

 from that, for instance, adopted in H. and A. Adam's " Genera." 



Those authors associated with the first named family the Glauconomyid^ which 

 I have placed in the MYA GFA, stating the reasons for that transfer (see p. 89). The 

 Veneridm are divided into four sub-families, TAVEsmm, venerin2e, sunettinm, and 

 JDOSINIIN.E, the first of which I consider to be the nearest allies to the Fetricolidm, 

 The family Glossidm has been made to include besides Glossus (= Isocardia, Lam.,) 

 Trapezium, Goralliophaga, and several other allied genera which were formerly 

 referred to the tapesin^, also Cyprina and its allies for which H. and A. Adams 



