582 kiiynchonellidje. 



Fam. RHYNCHONELLIDiE. 



Oral arms elongate, flesliy, spiral, supported at the base 

 by two short, curved, shelly, diverging laminae arising from 

 the hinge-margin of the ventral valve. 



Shell not punctate, usually tetrahedral and sharply pli- 

 cate ; the interior without any shelly plates or cartilaginous 

 or testaceous skeleton. 



In this family the spirally convoluted buccal appendages 

 or oral arms are not supported by any internal apophysary 

 system, the substance of the shell is not punctate, and its 

 surface is generally plaited. 



Genus RHYNCHONELLA, Fischer. 



Shell tumid, thin, variable in shape ; beak of upper or 

 ventral valve acute, entire, more or less recurved ; no true 

 area ; foramen triangular and open, placed under the beak, 

 reaching the margin. Apophysary system consisting of 

 two separate, curved, moderately developed, shelly blades 

 projecting from the hinge of the lower or dorsal valve. 



Syn. Hypothyris, Phillips. Hermithyris, D'Orb. 



Ex. E. psittacea, Chemnitz, pi. 132, fig. 2. Shell, R. 

 psittacea, fig. 2, a, 2, b. 



The shell in this genus is never punctate, and the free, 

 fleshy, spiral arms are affixed to two short, flattened, and 

 grooved lamellse, separated from each other, slightly curved 

 upwards, and attached to the inner side of the beak of the 

 small dorsal or imperforate valve. Three recent species are 

 known; R. psittacea is from the northern and arctic seas, 

 and R. nigricans is from the shores of New Zealand. 



