26 



Remarks : — The comparatively long and narrow shell and the truncate extremities 

 distinguish M. erj'onea from other species of the genus. 



3. Malletia encrypta sp. nov. (Plate I, figs. 44, 45). 



The following is a description of this new species: — Shell of médium size, moderately 

 thick, oblong, very tumid; obliquely rounded anteriorly, subtruncate posteriorly, anterior dorsal 

 slope greatly arcuate, posterior almost straight; ventral margin slightly arched ; subequilateral ; 

 umbones very convex, tumid, sculpture consisting of very regular, close-set, concentric striae; 

 hinge-plate moderately strong, with about 14 teeth anterior to and 22 posterior to umbo. Shell 

 very glossy, pale straw coloured ; nacre dull white. 



Measurements of Holotype: — Length 13 mm., height 9 mm., diameter 6.6 mm. 



Habitat: — The unique Holotype of M. encrypta was brought up in a deep-sea trawl 

 at St. 178 (2° 40' S., i28°37'.5E., 835 mètres). 



Remarks : — M. encrypta exhibits a superficial resemblance to M. dunkeri Smith ^), but 

 the form of the shell, the sculpture and the more extensive hinge are distinctive. 



4. Malletia humilior sp. nov. (Plate VIII, figs. 3, 4). 



The following is a description of this new species: — Shell of small size, thick, oblong, 

 somewhat swollen ; sharply rounded at anterior end, broader behind, slightly rostrate above ; 

 obliquely truncated posteriorly; dorsal slope almost straight, ventral margin arcuate; umbones 

 small, subcentral, greatly raised above dorsal margin ; sculpture consisting of very regular, low 

 concentric ridges; two radial ridges indicated on posterior slope-, hinge-plate moderately developed; 

 about 12 teeth anterior to and 16 posterior to umbo. Shell pale yellow, nacre shining white. 



Measurements of Holotype: — Length 6.4 mm. height 4.5 mm., diameter 3.5 mm. 



Habitat: — Two shells of M. Jniniilior were brought up in a deep-sea trawl at St. 88 

 (o°34'.6N., ii9°8'.5E., 1301 mètres). 



Remarks : — The small size, very regular sculpture and the slightly rostrate posterior 

 upper margin of the shell distinguish this species. 



5. Malletia tripartita sp. nov. (Plate I, figs. 46, 47). 



The following is a description of this new species : — Shell of médium size, thin, oblong, 

 subquadrate, moderately, tumid, rounded at anterior end, subtruncate posteriorly ; anterior dorsal 

 slope slightly arched, posterior slope greatly curved -, umbones small, acutely rounded, not very 

 raised above dorsal margin ; sculpture consisting of well marked but shallow, rounded ridges 

 on only a quadrate area in middle of shell, almost smooth on both ends ; hinge-plate moderately 

 strong, with about 14 teeth anterior to and 20 posterior to umbo. Shell light yellow; nacre 

 shining yellowish white. 



Measurements of Holotype: - — Length 7.4mm., height 5 mm., diameter 3.5 mm. 



l) Smith, E. A. — "Challenger" Lamellibranchia, p. 323 (1885). 



