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



Nucvla sp. 



Habitat. — Station 191, off the Arrou Islands, in 800 fathoms; green mud. 



Only a single dead valve of this species was discovered, and that not in a good state 

 of preservation. Its existence is worthy of record, as indicating the presence at this 

 locality of a large species which in many respects closely resembles the Nucula 

 decussata of Europe. It is perhaps a trifle flatter than that form, and tlie anterior side 

 in the region of the hmule is rather more concave, but the external sculpture is about 

 the same. The hinge-plate and the teeth appear to be less strongly developed, and tln' 

 outer or ventral margin is not quite so distinctly lirate within. 



The valve under examination is 22 mm. in length and 18^ in height. 



Nucula niponica, n. sp. (PI. XYIII. figs. 8-8«). 



Testa magna, tenuis, ovalis, valde insequilateralis, epidermide nitida olivacea induta, 

 incremeuti lineis tenuibus striata, lineis paucis radiantibus obsoletis impressa. Lunula 

 inconspicua, imjjressione hand profunda circumdata. Umboues pallidi, couvoluti, circa 

 in \ longitudinis totius positi. Pagina interna iridescens, cseruleo-margaritacea, 

 radiatim tenuissime substriata, ad niarginem acuta et Integra. Fossa ligamenti profuoda, 

 intra vulvas oblique projecta. Dentes elongati, acuti, in numero circa 25, quorum octo 

 ante umbones sunt. 



This is a fine large species, comparatively thin, of an oval form, the anterior extremity 

 being just a trifle more acute than the j)osterior. It is very inequilateral, and clothed 

 with a highly glossy olivaceous epidermis, which is paler towards the umbones, and 

 exhibits, at irregular intervals, narrow, concentric, darker zones. The sculpture consists 

 of fine lines of growth (some of them amounting to shallow concentric grooves) and 

 several feebly expressed radiating impressed lines. The lunule is rather long, 

 prominent along the middle, not clearly defined, but only marked ofi" by a shallow 

 depression, and occupies the greater part of the anterior slope. The beaks are pale, 

 small, incurved, and located at barely one-fourth of the total length from the anterior 

 end. The interior is iridescent pearly, the predominant colour being blue. It exhibits a 

 very minute radiating substriation, and is surrounded by a sharp, simple, non-crenate 

 edge. The hinge-teeth are fairly strong, longish, acute, about twenty-five in number, of 

 which only eight are in front of the deep, oblique, inwardly projecting ligament-j)it. 



Length 22 mm., height 15, diameter 9. 



Habitat. — Station 232, south of the Island of Nipon, Japan, in 345 fathoms ; green 

 mud. 



