402 PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



larger outer lateral;* uncini numerous (50-150), similar, hooked at the 

 tip, those of each lateral series springing from a common base. 

 1 



Formula: 



m (1+3-3+1) m 



This family differs from its nearest described allies (the Fissurellidcv) 

 in its single asymmetrical gill, in the absence of appendages to the 

 sides of the foot or on the mantle edge, and in its i)atelliforui, unflssnred, 

 unsinuated, and wholly external shell. 



From the succeeding family, Addisoniidce^ it is separated by its sym- 

 metry, the character of tbe gills, and by its dentition. By its dentition 

 it is most nearly allied to Parmophorus or Sciotus, if figures be taken as 

 a criterion (and much resembles some species of Helicina), but it must 

 be borne in mind that very few species of Fissurellidcc, have been figured 

 in proportion to the whole number known. The other characters, how- 

 ever, forbid its incorporation with the FissurelUdcc as they conflict in 

 nearly every important feature with the definition appropriate to that 

 family. 



At first it was thought that Propilidium might be incorporated in this 

 family, but an examination of the available data relative to that genus 

 indicates that it belongs rather in the FissKrellidw, where it, api)ar- 

 ently, represents an imperforate Piincturella. 



Genus Cocculina Dall. 



Animal blind; shell colorless, with radiating and concentric sculpture; 

 for other characters see diagnosis of family. 



Cocculina Rathbuni, u. s. 



Shell depressed, white, thin, with sides nearly parallel and their slopes 

 lightly flattened, and with ends similarly broadly rounded ; sculpture 

 of fiiint closely (but irregularly) set grooves radiating from a smooth 

 apex (which has originally a subspiral nucleus) and crossed by concentric 

 growth lines, which are more or less irregular in different individuals ; 

 faint yellowish areas seem to indicate a thin, very closely adherent 

 epidermis ; apex prominent, more or less incurved and slightly laterally 

 compressed, usually showing a scar where the embryonic nucleus was 

 attached; inside polished or smooth ; length 11.0; width 0.5 ; altitude 

 2.75'"™. Another dead specimen is three times larger. 



Soft parts: Foot ovate, thin, not very high, somewhat pointed behind; 

 mantle margin moderately wide with a thickened i)lain border; behind, 

 on each side of the " tail," between the mantle and foot, is one cylindrical 

 blunt filament; sinus above the head and neck quite deep; gill exactly 

 as in Acmaa, t-mall, hardly projecting out of the sinus; head large, end of 

 muzzle semi-lunate, with a strongly marked margin ; in the midst of this 

 flat lunate area is a rounded papillose space surrounding the mouth; this 



* Much as iu Scutus as figured by Gray, Guide, ji. 103. 



