REPORT ON THE liAMELLlBRANCHIATA. 223 



maintain that the former species is absohxtcly ideuti(';il with Crassatella, hence the 

 disappearance of (Touldla from conchology. Dall holds tluit the hitter species is 

 generically distinct from Circe " on conchological grounds alone." This I deny, and am 

 of opinion that it possesses at most sectional or subgeueric rank, and may therefore be 

 placed in Lioconcha if this separation be thought advisal)le. To give names to such 

 minor sections, if they be fiiirly recognisable, is 1 think alIowal)le, and to a certain 

 extent useful in those genera which contiiin a large numl)('r of species, but in sninll 

 groups this practice should not Ix' encouraged. 



Crassatella torresi, n. sp. (PI. XVI. figs. 2-2a). 



Testa parva, valde compressa, tenuis, alba, trigona, costis concentricis paucis postice 

 incrassatis et productis instructa. Margines dorsi valde declives, fere sequales, antico 

 levissime concavo, postico vix convexo ; margo ventralis maxim e curvatus. Umbones 

 parvi acuti, mediani. Dens cardinalis unicus in valva dextra, duo in sinistra ; laterales 

 utrinque perremoti. Ligamentum angustum, in sulco marginali locatum, partim 

 internum, in fossa parva. infra apices positum. 



This little species is very compressed, equilateral, quadrant-shaped, thin, semi- 

 transparent, white, and ornamented with about a dozen rather remote concentric ridges. 

 They are thickened at their posterior extremities and a trifle prolonged into scale-like 

 projections, forming a crest along the dorsal margin. Between the costse very fine 

 radiating striaj are discernible under the microscope. The dorsal margins are of equal 

 length, and form almost a right angle at the apex. The anterior is the least concave, and 

 the posterior the slightest excurved. There is a single central longish cardinal tooth in 

 the right valve, which fits in between two equally long ones (of which the posterior is 

 rather the larger) in the left, and the former valve exhibits a distinct very remote lateral 

 on each side, separated from the outer margin by a conspicuous furrow which receives 

 the prominent lateral margins of the other valve. The slender ligament is situated in a 

 narrow posterior marginal groove, and a small portion of it is internal and located in a 

 very small pit Ijeneath the beaks and just posterior to the cardinal teeth. The interior of 

 the valves is smooth and glossy, and owing to their trans^^arency exhibits the external 

 ribbing. The outer margin is simple, smooth, and non-creuate. The muscular scars 

 and pallial line are not clearly definite. 



Length 3^ mm., height 3^, diameter 1. 



Habitat. — Station 188. south of New Guinea, in 28 fothoms green mud. 



The single minute shell here characterised may not be, and probably is not, adult, but 

 is sufficiently distinct and pecidiar to merit description. 



