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



Length 29 mm., height 14, diameter 12. 



Habitat. — Station 305, west coast of Patagonia, in 165 fathoms ; l)lue mud. 



Both this species and Neceixt woUastonii may eventually prove to be large varieties 

 of Ne(Bra rostrata, Spengler, being similarly sculptured. Still there is a considerable 

 difference in form. The single left valve from the above locality has the apex of the 

 umbo (viewing it from within) situated 13 mm. from the anterior end, or only one 

 and a half in advance of the centre. From this it will be seen that it is more equilateral 

 than Necera rostrata, but less so than Necera woUastonii. 



NecBra ivollastonii, n. sp. (PI. X. figs. (j-Qh). 



Testa magna, tenuis, alba, hand nitida, globosa, ovata, postice louge rostrata, incre- 

 ment! lineis tenuibus striata. Margo dorsi auticus oblique arcuatus, posticus minus 

 declivis, levissime concavus. Ventris margo antice et inferne late arcuatus, ad rostrum 

 late sinuatus. Rostrum elongatum, marginibi;s subparallelis, carina obliqua leviter 

 curvata dimidiatum, ad extremitatem posticam subrecte truncatum. Umbones magui, 

 involuti, ad apicem sublsevigati, centrales. Pagina interna nitens, plus minusve radiatim 

 substriata. Linea cardinis tenuis, subreflexa, sub umbone valvae sinistra^ loculo 

 ligamentali parvo obliquo instructa. 



This is a large thin shell, much inflated, ovate, and terminated behind in a long beak. 

 It is white, with scarcely any gloss upon the surface, and sculptured with fine striae of 

 growth only. The hinder dorsal margin is slightly oblique and the least concave, the 

 anterior being arcuate and more sloping, but this depends u^ion the position in which the 

 shell is regarded. The anterior end is semicircularly rounded, the ventral outline more 

 broadly curved and widely sinuated at the commencement of the rostrum. This has the 

 upper and inferior margins almost parallel, the extremity nearly abruptly truncate, and is 

 obliquely bisected by a slight radiating ridge. The umbones are considerabl}^ elevated, 

 exactly central, smoothish, and incurved at the tips. The hinge-line in the left valve is 

 thin, a little expanded upwards on both sides of the umbo, immediately beneath which is 

 a very small ligamental pit directed obliquely towards the hinder end. The interior is 

 glossy,, and exhibits a distinct substriation about the central parts. The posterior 

 muscular scar is elongate, and situated under the dorsal line not quite half-way from the 

 umbo to the end of the rostrum. 



Length 26 mm., height 14^, presumed diameter of the complete shell 12. 



Habitat. — Station 73, a little west of the Azores, in 1000 fathoms ; Pteropod ooze. 



I have named this species in remembrance of the late T. V. Wollaston, who contri- 

 buted so much to our knowledge of the fauna of the islands of the Atlantic. It is a 



