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



of growtli. The front dorsal margiu is long, scarcely at all oblique, and only very faintly 

 excui-ved. The hinder slope is very much shorter, much more sloping and more curved. 

 The ventral outline is widely curved, without any sinuation. The umbones stand out a 

 little above the dorsal margin, are situated about one-third of the total length from the 

 posterior end, and terminate in a minute obtuse apex. There is in the right valve a 

 single tubercular tooth beneath the umbo, and an elongate groove within the margin on 

 the anterior side, for the reception of the raised edge of the opposing valve. Within 

 the posterior margin, at a short distance from the apex, there is a slight denticular 

 prominence, beneath which is found the oblique groove containing the internal ligament 

 which extends as far as the anterior denticles. In the left there is scarcely any indica- 

 tion of teeth, but the denticular prominence on the posterior side, supporting the 

 ligament, is fairly conspicuous. The muscular scars and the pallial impression are 

 indistinct. 



Length 6^ mm., height 4, diameter 2f. *" 



Habitat. — Station 75, off Fayal, Azores, in 450 fathoms, volcanic mud; and Station 

 VIIL, oif Gomera, Canaries, in G20 fathoms, volcanic mud. 



This curious little species is remarkable for its oblong, inequilateral form, and is quite 

 distinct from Montacuta cylindracea, which is proportionally less elongate, has a shorter 

 internal ligament, and only the faintest indication of a groove within the anterior dorsal 

 margin of the right valve. 



In form this species closely resembles Montacuta ferruginosa, Montagu, but is rather 

 more convex, has more prominent beaks, and different hinge-characters. 



Famdy S o l e M y i d ^. 

 Solemya, Lamarck. 



Solemi/a patagonica, n. sp. (PL XL figs. l-lo). 



Testa oblonga, postice paulo angustata, antice sensim latior, arcuatim truncata, 

 epidermide crassa, nigro fusca, radiatim lirata et sulcata, ad marginem profunde scissa 

 longeque extra valvas producta, induta. Linea dorsi ante umbones intus incx-assata, 

 'densatione paulo ante medium aliquanto intra marginem producta. Pagina interna 

 radiatim obsolete subcostata, costa obliqua submediaua cseteris majore. Cicatrix postica 

 profunda, oblonga, inferne linea elevata marginem dorsalem anticum versus producta, 

 marginata ; cicatrix antica magna, subpyriformis. 



Length 31 mm., height 11, diameter 6. 



Habitat. — Station 311, off west coast of South Patagonia, in 245 fathoms. 



This is very like other species of the genus in general appearance, but may be 



