JUKES-BEOWNE : CKETACEOUS AND EOCENE VENEKID^. 153 



For some time I was inclined to agree with M. Cossmann in 

 considering C. incrassata to be a Pitaria, but a more careful study of 

 a large number of interiors and a comparison with C. Lyelli from the 

 Hamstead Beds have convinced me that both species are more nearly- 

 related to Bosinia. C. Lyelli is, in fact, still more Bosifiia-\ikQ than 

 C. incrassata, having a very small lateral tooth and a very shallow 

 pit, while in the right valve the anterior cardinal is directed forward 

 as in so many species of Bosinia. 



I am consequently of opinion that these shells are ancestors of 

 Bosinia, and that B. trigona and its congeners are direct descendants 

 of the ancestral form which have persisted to the present day. 

 Seeing also that they differ in so many ways from Bosinia proper, it 

 seems desirable that they should be separated as a distinct subgenus 

 under a new name. For this I propose Sinodia, which is an anagram 

 of Bosinia, and for the type I take B. trigona (Reeve) (see Fig. 1), 

 hoping that the animal may soon be examined to see if it also differs 

 from that of Bosinia. 



So far as I can ascertain, no true Bosinia has yet been discovered 

 either in Cretaceous or Eocene strata, the B. cretacea of Zittel (1864) 

 being either a Cyprimeria or a Cyclorisma, and the ' Bosinia sp.' of 

 Holzapfel (1889) being only so named from the resemblance in 

 external shape. A true Bosinia has, however, been described from 

 the Oligocene of Florida by Dr. Dall. 



If my view be correct, the typical orbicular form of Bosinia, with 

 its deeply impressed lunule, is a specialized and comparatively recent 

 type, not appearing in AVestern Europe until the Miocene epoch, 

 while Sinodia was specially prevalent in Oligocene time, and was 

 probably developed from Pitaria, which certainly existed in eaily 

 Eocene times. I find this latter view is in accord with the opinion 

 expressed by Stoliczka,^ who suggested a connection between Bosinia 

 and Caryatis (i.e. Pitaria) through the species B. trigona and 

 B. sph(Bricula. Moreover, in most Pitaria, in the Eocene Atopodonta, 

 and in the cognate Callocardia, the teeth are arranged in a manner 

 which resembles that described by Bernard as occurring at a certain 

 stage in the development of the hinge, the special point being that 

 the right anterior cardinal and the front half of the bifid posterior 

 cardinal are connected by a curved lamina which forms an arch over 

 the median tooth. 



The characters of the Sinodia group have practically been given 

 above in distinguishing it from Bosinia, but it may be useful to 

 indicate the points in which it differs from Pitaria or the latter from 

 it. Pitaria is generally of a more regularly oval shape ; it has 

 a larger lateral pit in the right valve with more or less well developed 

 lateral teeth above and below ; the anterior cardinal is always parallel 

 to the median, but is connected with the posterior in the manner 

 above-mentioned. The pallial sinus is so variable that no distinctive 

 character can be based upon it. 



1 " Cretaceous Fauna of Southern India," vol. iii, Pelecypoda : Pal. Indica, 1S71, 

 p. 155. 



VOL. VIII. — OCTOBER, 1908. 13 



