158 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



5. PiTARiA, Eoemer, emend. Dall. PI. VI, Fig. 3. 



This group was founded by Roemer in 1857 under the name ' Pitar' 

 (after Adanson), but in 1862 he proposed to substitute the name 

 Caryatis; this, however, is preoccupied in Lepidoptera (Hubner, 1816), 

 and Dr. Dall has very properly pointed out that Roemer' s original 

 name should be adopted and Latinized into Pitaria^ just as the 

 'Dosin' of Adanson was converted into Bosinia. 



The type of this group is Venus tumetis, Gmelin, and the species 

 belonging to it were included by Gray in his genus Btone (1847), 

 which name is also preoccupied by Hubner. The division was 

 recognized by Cossmann in 1886 under the name of Caryatis, as 

 represented by many species in the Eocene of France. 



Pitaria has an oval shell which is smooth or finely striate ; the 

 Innule is circumscribed and superficial, not impressed. The hinge has 

 already been partly described, but it may be added that the median 

 and anterior cardinals of the left valve are united at the top, and are 

 separated from the shell-border by a sulcus or channel, into which fits 

 the arch formed by the union of the anterior and posterior teeth of the 

 right valve. The strength of the bridge in the right valve and the 

 consequent breadth of the corresponding channel in the left valve vary 

 considerably both in recent and fossil species. Lastly, the anterior 

 cardinal of the right is short and is undercut by a channel connecting 

 the anterior lateral pit with the socket between the anterior and 

 median cardinals. The pallial sinus is variable, sometimes small and 

 sometimes deep, sometimes pointed and in others rounded, but generally 

 ascending. 



Species referable to Pitaria are believed to occur in Cretaceous 

 rocks, but I have not been able to recognize any among those from 

 English Cretaceous deposits. Many species from the Lower Cretaceous 

 of France are still only known from casts, and consequently they 

 cannot be referred to their proper genera. Venus Orbigniana, Forbes, 

 may possibly be a Pitaria, but neither Mr. Woods nor I have been able to 

 obtain sight of a specimen that shows the interior. Stoliczka supposed 

 that V. Rotomagensis, d'Orb., was a Pitaria, and he may be right, but 

 again we have not yet succeeded in seeing one which shows the hinge 

 of either valve. 



Many species of Pitaria occur in the Eocene, the commonest and 

 best known being P. Parisiensis, Desh., and P. oUiqua, Desh., though 

 both have always been catalogued in this country as ' Oytherea.'' 

 Cyth. incurvata (Edw. MS.) is also a well-characterized species of 

 Pitaria, remarkable for its transverse elongation and for its prominent 

 recurved umbones. C. transversa, Sow., C. Bartonensis (Edw. MS.), 

 and C. striatula, Desh., also seem to belong to Pitaria. 



6. Atopodonta, Cossmann. 



This name was proposed by M. Cossmann in 1886 (op. cit., p. 110) 

 for two small shells occurring in the Parisian Eocene, the first and 

 type being Venus conformis, Desh., and the second A. tapina, Cossm. 

 (then first described). 



