394 RINGICULA. 



1864. GILL, Smiths. Misc. Coll., No. 227, p. 14. FISCHER, Man. 

 de Conch., p. 56] . 



Shell short and ventricose, with conic spire of several whorls ; 

 aperture narrow, obstructed by folds on the columellar margin ; 

 peristome thickened outside, often dentate within. Operculum 

 wanting. 



Animal completely retractile within the shell, with short foot> 

 head-disc wide, prolonged backward in the middle, a sort of siphon 

 being formed by the rolled-in margins; radula without central 

 tooth, laterals two, arcuate, the cusps directed inwards. (See pi. 46, 

 fig. 49). 



In the recent fauna this family is represented by but one genus, 

 Ringicula. There are several fossil groups, Avellana, Cinulia, 

 Oligoptycha, etc. (See Struct, and Syst. Conch.). 



Genus RINGICULA Deshayes, 1838. 



Ringicula DH., Hist. Nat. Anim. s. Vert., 2d edit., viii, p. 323, 

 1838, type Auricula ringens Lam. MORLET, Journ. de Conchyli- 

 ologie 1878, pp. 113, 251; 1880, p. 150: 1882, p. 200 (illustrated 

 monograph of recent and fossil species). Ringiculina MONTEROSATO 

 Norn. Gen. e Spec., p. 141, type R. leptocheila (1884). 



Shell small, solid, nearly white, ovate-globose, the spire conical ; 

 aperture from one-half to three-fourths the shell's length, conspicu- 

 ously notched and channelled at base ; outer lip thickened and 

 often dentate or crenulated within, margined with callus outside ; 

 columellar margin heavily calloused, with two to four strong enter- 

 ing folds. Type R. ringens Lam. 



Jaws as in Akera, etc. 



The animal is peculiar in the very broad head-disk produced in 

 a sort of siphon in the middle behind. The dentition closely re- 

 sembles that of Philine and the Scaphandridce. 



Ringicula ranges over nearly all tropical and subtropical seas. 

 In the geological series it extends to the base of the Eocene with a 

 few forms in the Cretaceous, but below the Tertiary the group ia 

 represented mainly by Cinulia and Avellana. About 42 recent and 

 75 fossil species have been described. 



Morlet divides the group as follows ; the fossil species are not here 

 enumerated : 



