472 Zoological Society. 



A species nearly allied to the S. amhiguus of Lamarck, from -which 

 however it differs, both in its greater curvature and in the absence 

 of the discal rays which adorn that species. Its breadth is through- 

 out equal, and the umbones are considerably flattened. 



SoLEN ACiNACES. Sol. testd Uueari, nived, suhdepressd, arcuatd, 

 postic^ ahruptd, antice attenuatd, rotundatd; latitudine longitudinem 

 prope quadruplb superante ; margine postico vix convexo ; epider- 

 mide nitidd fiavescente ^ car dine terminali, dente in utrdque valvd, 

 unico, rotundato. Long. J ; lat. 3 poll. 



Hah. } 



A shell scarcely to be confounded with any of this genus, but with 

 somewhat the aspect of >S'. scalprum. 



SoLEN CYLiNDRACEUs. SoJ. tcstd Uncari, rectd, cylindraced, sub 

 epidermide fugaci, alhd, ruhido-purpurascente variegatd ; latitu- 

 dine longitudinem sextuplo superante ; margine antic^ rotundato- 

 obtuso, postic'h abrupto, concavo ; cardine terminali, dente sub- 

 lunari in utrdque valvd prominente. Long. J ; lat. 3 poll. 



Hab. } 



A tolerably strong shell, intermediate between the S. linearis of 

 Wood and the S. brevis of my descriptive Catalogue. The former 

 species is considerably narrower from the umbones to the ventral 

 margin, these proportions being precisely reversed in the latter. 

 The colouring likewise, which in the adult is almost entirely confined 

 to the posterior half, differs from its arrangement in the S. brevis. 



Mesodesma triquetrum. Mes. testd oblique triangularis vald^ 

 incequilaterali, crassissimd, tumidd, laviusculd, sordide albidd;pos- 

 tic^ brevi, rotundatd, antice productd, subacuminatd, subrostratd ; 

 margine antico declivi, ventrali arcuato ; pube depressd ; foved liga- 

 mentali inter nates distantes plane hiante ; dentibus lateralibus 

 magnis, validis. Long. J ; lat. 1 poll. 



Hab. ? 



I know of no species which could possibly be confused with this 

 extraordinary shell, which, from the peculiar triangular cavity be- 

 tween the beaks (as in the genus Schizodesma of Gray), may even- 

 tually prove the type of at least a subgenus. In the unique speci- 

 men before me there is the appearance of ochraceous rays, but I do 

 not venture to consider them as characteristic until the comparison 

 with further specimens. The shape reminds one of Mulinia Donaci- 

 formis. The cardinal tooth is bifid in the left valve. 



Mesodesma planum. Mes. testd ovato-sublenticulari, transversd, 

 valde compressd, incequilaterali, utrdque extremitate rotundatd; 

 sub epidermide corned, albidd, lavigatd ; natibus elevatis, acutis ; 

 margine ventrali arcuato ; foved ligamentali angustd. Long, f ; 

 lat. 1 poll. 



Hab. ? 



A pecuharly flat shell, which is not unlike M. complanatum, but 

 differs as well in the colouring of its epidermis as in many other 

 particulars. From the little convexity of the dorsal margins, the 



