266 CEETACEOUS PELECYPODA 



striated; hinge with three teeth in the left valve, two small anterior and one 

 somewhat remote and elongated posterior, right valye with only two diverging 

 elongated cardinal teeth ; cartilage situated in a groove in front of the posterior 

 teeth; mnscular impressions faintly marked; type, B, corhuloides, Phil., occurs 

 recent in the Mediterranean and the Atlantic, and fossil in miocene beds of Italy 

 and the Vienna basin. 



Ohenu figures the animal of this species as JErycina Geoffroyi, (Man., ii, 

 p. 124), which shows that tlie prolonged foot and the mantle fold are quite different 

 from either Lepton or Lascea. 



11. Fythina, Hinds, 1844. Shell oval or roundish, with radiating or divaricate 

 striae or sulci on the surface ; right valve with two, left with three, cardinal teeth, 

 the outer one diverging and elongated, cartilage small in front of the posterior 

 teeth ; type, P. Deshayesiana, H. The hinge of this genus is exactly the same as 

 that of Bornia, from which BijtUna only differs by its peculiar divaricate striation. 



12. Cyamium, Philippi, 1845. Shell oblong, inequilateral, slightly gaping 

 or closed ; hinge with two sub-anterior cardinal teeth in each valve, the anterior 

 being produced and lamellar ; cartilage internal, situated in a groove behind the 

 teeth, and ligament external, supported by distinct fulcra; pallial line truncate 

 behind ; type, (7. antarcticum. 



H. and A. Adams (Genera ii, p. 651,) suggest that Tiirtonia with the type 

 T, minuta, Eab., should be kept distinct from Cyamium proper, but Jeffreys (Brit. 

 Conch., ii, 257,) states that he carefully examined numerous specimens of both 

 species and believes them to belong to the same genus. Perfect specimens of 

 (7. antarcticum, he says, are closed at both ends. 



13. Hindsiella, Stol., 1870, (mndsia, Desh., 1860, Paris foss., 2nd ed., i, 

 p. 693 — non Emdsia, H. and A. Adams, 1850). Shell elongately sub-triangular, 

 nearly equivalve, with the lower margin insinuated, hinge with one or two 

 (generally one in the right, two in the left) minute cardinal teeth in each valve ; 

 ligament external, supported by thin fulcra; muscular impressions narrow, 

 elongated, pallial line rather broad, simple; type, Modiola arcuata, Defr., from the 

 eocene of the Paris basin. 



Deshayes alludes to the close relation of this genus to FytUna ; it also 

 recalls the form of Cyamium, which has an external ligament, and the hinge-teeth 

 are in structure somewhat allied to LascEa ; but as there is apparently no cartilage 

 present, it appears probable that the genus could be more correctly classed next 

 to Modiolarca, Gray, in the family Glossidje (vide p. 184). 



14. Thecodonta, A. Ad., 1864, (Ann. Mag. Nat. Hist., xiii, p. 308). Shell 

 oblong, very inequ.ilateral, the anterior part being shorter than the posterior, con- 

 centrically sulcated ; hinge in the left valve with two diverging cardinal teeth with 

 a cup-like projecting fold between them, a single posterior lateral tooth present; 

 pallial line single and radiately grooved, anterior muscular scar triangular, posterior 

 oval; type, Th. Sieholdi, A. Ad., from the China seas. The right valve of this 

 remarkable shell, which recalls the form of Seterocardia, has not as yet been seen, 



