266 CRETACEOUS PELECYPODA 



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

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

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

 teeth; muscular impi'essions faintly marked; type, JB. corhulokles, Phil., occurs 

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

 and the Vienna basin. 



Clienu figures the animal of this species as Enjcina Geoffroyi, (Man., ii, 

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

 from either Lcpfon or Las(va. 



11. Tijtluna, Hinds, ISli. Shell oval or roundish, with radiating or divaricate 

 strite or sulci on the siu-face ; 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 Pythina only dijffers by its peculiar divaricate striation. 



12. CyamUtm, 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 ; tyj)e, C. antarcticuni. 



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

 T. mimita, Eab., should be kept distinct from Cyainhim j)roper, 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 

 C. untarcticum, he says, are closed at both ends. 



13. ninclsiella, StoL, 1870, (mndsia, Desh., 1800, Paris foss., 2nd ed., i, 

 ]). 693 — non Hbidsia, 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 teetli 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 genvis to Pythhia ; it also 

 recalls the form of Cyamlmn, 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, Gvvij, in the family Glossid^ (vide p. 184). 



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

 oblong, very inequilateral, the anterior part being shorter than the posterior, con- 

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

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

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

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

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



