OP SOUTHERN INDIA. 263 



XXV. Family,— EB YCINIDuE. 



The animals have the mantle margins below open, either entire or provided 

 with filaments, and often greatly extensible beyond the edges of the shell; in 

 front the margins form a more or less distinct open fold which represents the inha- 

 lant siphon, the exhalant siphon is situated posteriorly, and prolonged into a more 

 or less spacious tube ; the foot is large, generally with a grooved and expansible 

 sole, often bent upwards and posteriorly provided with a small byssus ; there is a 

 pair of gills and one pair of palpi on either side. 



The shells are of small size, oval, or sub-triangular, thin, equ.ivalve, closed, 

 generally inequilateral, with the surface smooth or finely ornamented and often 

 covered with a polished epidermis ; the hinge is provided with strongly divero^ino- 

 cardinal and sometimes also with lateral teeth ; the cartilage is internal, situated 

 between the teeth ; two muscular impressions ; pallial line entire. 



The JEuYcimBM form a very natural group of small shells, mostly living on 

 sandy or gravelly ground at considerable depth of sea ; their geographical distri- 

 bution is general. Almost a larger number is known from northern than from 

 other seas, but, the tropical regions having as yet been only very little explored 

 with the dredge, it is difficult to form a correct conclusion on the distribution of 

 the family. 



The present number of recent species is scarcely as large as that known from 

 the Paris basin alone, aad if other eocene deposits are equally, or nearly so, rich, 

 it would certainly appear that the family then possessed its greatest development. 

 Prom cretaceous rocks only one species has been recorded ; others do not appear 

 to be satisfactorily determined, and those noticed from older formations under the 

 names of Urycina, and others, are perfectly unreliable. 



The genera to be placed in the present family are Brycina r=^Kellia), 

 Erycinella, Spaniodon, Montacula, TelUmya, Kelliella, Lascea r= Poronia), Lep- 

 ton, Fristiphora, Boriiia, Pythifia, Cyamiiun, Hindsiella, Thecodonta. H. and 

 A. Adams class the genera Avhich among those just noted occur recent in two 

 families, separating Lepton from JErycina as types, but I do not think that the 

 slight prolongation of the mantle and its marginal filaments are sufficient to 

 justify such a separation. 



1. JErycina, Lam., 1804, ( Kellia, Turton, 1822, Chironia, Desh., 1839). 

 Shell oval, generally somewhat elongated, sub-equivalve, moderately , inflated, 

 concentrically striated, or with more or less distinct radiating ribs ; hinge wdth 

 tw^o widely diverging, large, often grooved or divided cardinal* teeth, sometimes 

 there is a minute tooth immediately under the beak, but more often it is obsolete 

 in both, or, at least, in the right valve. Cartilage situated in an internal groove, 

 extending from the beak posteriorly and situated in front of the posterior tooth ; 

 type, U. pelhicida, Lam., from eocene beds of the Paris basin. 



* In some of the species the posterior tooth is rather remote, but it always originates near the beak, and ahould, 

 therefore, be more properly called a cardinal than a lateral tooth, under which name it is generally quoted in concho- 

 logical works. 



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