282 CRETACEOUS PELECYPODA 



elongated anterior muscular impression. Whether these differences hold good in a 

 comparison with the type species of the next genus appears very doubtful. 



32. Venericardia, Lam., 1801. Recluz in an account on the anatomy of Car- 

 dita and Venericardia (Journ. de Conch., 1862, vol. x, p. 109, &c.), considers as the 

 type of the latter genus V, australis? figured in Enc. meth., p. 232, fig. 5, and points 

 out that this species has a peculiar posterior partition in the mantle, in which there 

 is a single siphon included, and it has two pairs of gills on each side, while all the 

 Carditce, he states, have two siphons without a partition and only one gill on either 

 side. The shell is sub-trigonal, moderately inflated, radiately ribbed ; hinge with 

 one somewhat posterior cardinal tooth in the right, and two in the left valve, the 

 posterior being elongated, as in Cardita, According to this account there would 

 seem hardly any doubt as to the distinction of the animal of Venicardia australis 

 from that of Cardita, but it is still necessary to know something more of the char- 

 acters of the animals and shells of this and allied species before it is advisable 

 to make use of the distinctions indicated in the determination of shells alone. 



Eormerly such forms as Cardita antiquata, Linn., with a roundly trigonal 

 .shape, have been referred to Venericardia, but this character of form seems now 

 insuflSlcient, because in every other respect of shell-structure there is no essential 

 difference to be traced from the next genus. Hecluz says that the specimen 

 which he examined is from the Senegal. Should the species not be the same as 

 '' C ajar'' of Adanson, which is Blainville's type of Cardiocardita? This last 

 name has lately been again introduced by some American authors as a sub-genus 

 of Venericardia, but what its distinctive characters properly are I have not been 

 able to ascertain. 



Lamarck's type of Venericardia is apparently Venus imhricata, Gmelin, 

 a fossil species from Grignon. This, judging from Deshayes' figure in his first 

 edition of the Paris fossils, seems to be very closely allied to C onrad's Cyclo- 

 cardia, having two elongated oblique posteriorly directed cardinal teeth in the 

 left valve and a somewhat elongately oval anterior muscular impression. Now, it is 

 required to ascertain whether these (apparently not very important) characters 

 of the shell also occur in the form quoted by Recluz as Ven. australis^ and 

 whether this is the same as fCarditaJ ajar of Adanson. Should these suppositions 

 prove correct, Venericardia and Cardiocardita would be identical, and probably also 

 Cyclocardia, and Eecluz's examination of the animal would apparently confirm the 

 propriety of the generic distinction. But how many other fossil forms have to be 

 referred to Venericardia will depend from a further very careful examination and 

 comparison of the species. I do not think that we have as yet sufficient materials 

 to carry out Recluz' s suggestion to the effect, that Venericardia belongs to an 

 altogether different family from that of the Astaetid^. Some discrepancy cer- 

 tainly exists between his anatomical account and what I saw of the anatomy 

 of Cardita and Mytilicardia, and until many more species have been examined, 

 I do not think any generalisation of the conclusions will be very sound. What 

 should in such a case be, for instance, done with Gouldia, when compared with 



