REPORT ON THE LAMELLIBRANCHIATA. 49 



Section B. 



Necera curta, Jeffre3-s. 



Necera curta, Jeffreys, Ann. and Mag. Kat. Hist., 1876, .ser. 4, vol. xviii. p. 495. 

 Necera curta, Jeffreys, Troc. Zuol. Soo. Loud., 1881, p. 943, pi. Ix.xi. fi;.;. 10. 



Habitat. — Station 75, oft' the Azores, in 450 fathoms ; volcanic mud ; also 

 Station" 33, oft" Bermuda, in 435 fathoms ; other localities given by Jeffreys are 

 Stations 16 and 17, lat. 39° 55' N., long. 9° 56' AV., 994 fathoms; lat. 39° 42' N., 

 long. 9° 43' W., 1095 fathoms ; and 24 to 28a of the "Porcupine" Expedition, 1870. 



A single left valve from Station 33, measuring 9| mm. in length and 6^ in height, 

 agrees very closely with the figure cited aljove. This, too, is the specimen referred to 

 b}^ Jeffreys in the Proc. Zool. Soc. Lond. {loc. cit.). It exhibits one slight difference, 

 namely, in lacking the radiating striae on the anterior side. I think it likely that this 

 may be the same species as that referred Ijy Dall to Necera costellata (var. corpidenta)} 



A perfect shell containing the animal, from Station 75, shows that the right valve 

 is rather smaller than the left, the ventral margin of which projects slightly beyond the 

 other. 



Necera fallax, n. sp. (PI. X. figs, -l-'lh). 



Testa tenuissima, giobosa, antice acute rotundata, postice breviter ro.strata, incre- 

 menti lineis striata, liris radiantibus teuuibus postice instructa. Margo dorsi anticus 

 arcuatus, valde declivis, j^osticus paulo concavus, obliquus. Margo inferior late curvatus, 

 postice leviter sinuatus et crenulatus. Umbones leves, paulo post medium collocati. 

 Dens lateralis posticus valvse dextrse elongatus, uscj[ue ad rostrum productus. Pagina 

 interna subnitida, postice radiatim subsulcata. 



This species is rather globose, somewhat inequilateral, thin, narrowed to a sharply 

 rounded end in front, contracted and shortly beaked behind. It is .smooth towards the 

 umbones, sculptured elsewhere by fine lines of growth, and ornamented upon the hinder 

 half of the valves with aljout sixteen fine radiating lirae, of which those upon the 

 beaked extremity are the finest. The anterior dorsal outline is rather longer than the 

 posterior, much sloping and excurved, the hinder, on the contrary, being obliquely con- 

 cave. The ventral margin is broadly arcuate, with the exception of a faint sinuation at 

 the rostrum, where it is somewhat crenulated. The l)eaks are smooth, only slightly 

 prominent, and to the naked eye appear to have a posterior inclination, but in reality 

 are turned at the apex towards the front. The hinder lateral tooth of tlie right valve is 

 rather long, extending to the commencement of the narrowed extremity. The interior 



' Vide Bull. Mus. Comp. Zool., vol. ix., Xo. 2, p. 110. 

 (zOOL. CHALl,. EXP. PART XXXV. 188-5.) Mill 7 



