476 LASEID^E. 



Ex. P. Deshayesiana, Hinds, pi. 114, fig. 9, 9, a. 



The shell in Pythina is constricted towards the middle 

 of the ventral margin, causing the lateral portions to appear 

 as two lohes. The species are from America, New Ireland, 

 Australia, and the Philippines. 



Species of Pythina. 



arcuata, A. Adams. nucleus (Mactra), Conr. 



Cumingii, A. Adams. paula, A. Adams. 



Deshayesiana, Hinds. peculiaris, A. Adams. 



Deshayesii, D'Orb. and Reel. triangularis, A. Adams. 



Genus MONTACUTA, Turton. 



Shell small, thin, equivalve, inequilateral, transversely 

 ohlong; surface of valves radiately furrowed; beaks in- 

 flected; inner margins smooth. Hinge-margin with a tri- 

 gonal incision and cartilage-pit, and a pair of diverging 

 laminar teeth in one or both valves; ligament internal. 

 Pallial impression simple. 



Ex. M. substriata, Turton, pi. 114, fig. 10. Shell, M. 

 substriata, fig. 10, a, 10, b. 



The genus Montacuta differs from Kellia and La-sea in 

 a very remarkable manner. The fore-part of the mantle is 

 entirely destitute of the peculiar tubular processes found in 

 those genera; on which account Mr. W. Clark has con- 

 stituted for the genus a distinct family. 



Genus CYAMIUM, Philippi. 



Anal siphon slender and produced. Foot large, heeled. 

 Shell transverse, equivalve, thin, very inequilateral, 



