118 THE VOYAGE OF H.M.S. CHALLENGER. 



ceutral one most elevated, triangular, the hindmost being nearly as large, posteriorly 

 oblique, and somewhat bifid at the top. In the left valve both the anterior and posterior 

 teeth are slender, the central one being stout and distinctly bifid. The concentric lirse 

 are very fine at first, gradually increase with the growth of the shell, are rather sharp 

 and up-turned so that they are rough to the touch, the finger being passed from the 

 umbo downwards. They attenuate at the sides, and number about thirty-three in a 

 specimen measuring 9 mm. in height. The muscular impressions are subequal, the 

 anterior rather narrower than the posterior, and situated a little lower down. The sinus in 

 the pallial sear is small and angular. The crenulation of the margin is so fine that it is 

 only just visible to the naked eye, and commencing in front beneath the umbones extends 

 all round except along the posterior dorsal sloj^e. The ligament is wanting in all the 

 valves obtained, but is probably small, judging from the remains and the groove wherein 

 it rests. The colour within and without is either totally white or more or less stained 

 with purplish-rose in the umbonal region. 



Length 12^ mm., height 10, diameter Gf. Another specimen is 12 mm. long, 

 9^ high, and 6 in diameter. • 



Habitat. — Nightingale Island, Mid South Atlantic, 100 to 150 fathoms. 



This species recalls to mind the Venus gayi of Hupe, a Chilian and West Patagonian 

 species, which, contrary to that now described, has the hinder end more acuminate than 

 the anterior, the posterior slope more oblique, is rather more solid, has a more coarsely 

 creuulated inner margin to the valves, and less acute stronger concentric ridges. In 

 addition to these difi"erences there are others in the hinge, muscular scars, and pallial 

 sinus. 



Venus torresiana, Smith (PI. III. figs. l-lc). 



Venics torresiana, Smith, Eeport Zool. Coll. "Alert," p. 94, pi. vi. figs. M-M2. 



Testa transversa, antice rotundata, postice subtruncata, alba, obsolete rufo radiatim 

 maculata, ad apices et lunulam rufescens, concentrice lirata, infer liras radiatim striata, 

 paulo inajquilateralis. Margo dorsalis anterior arcuatus ad fijiem lunulse leviter incisus, 

 posterior paululum obliquus, rectiusculus, postice subangulatus. Extremitas antica 

 rotundata, postica arcuatim subtruncata, latior, ventralis late curvata. Lunula elongato- 

 cordiformis, perspicue circumscripta, concentrice lamellatim striata. Area angusta, 

 striata. Lamellae concentricse antice et in medio liriformes, postice tenues, elevatse. 

 Dentes cardinales tres in utraque valva, in dextra posteriori, in sinistra mediano aliquanto 

 bipartito. Sinus pallii mediocris, triangularis. Margo internus valvarum concinne 

 denticulatus. 



The form of this species is longer than high and somewhat inequilateral, the anterior 

 end being rather the shorter. TJie length increases much more than the height as the 



