428 MOLLUSCA. 
Unio LUTULENTUS (Gould). 
T. transversa, compressa, sub-falcata, valde inequilateralis, concentricé 
undulato-striata interdum nodosa vel sursum rugosa, fusco-virescens ; 
lateribus rotundatis ; marginibus sub-parallels ; apicibus prominu- 
ls, erosis ; dentibus cardinalibus obliquis, compressis, in valvd dextra 
bifidis ; dentibus lateralibus elongatis, compressis, rectis: margarita 
argentata ; limbo anticé incrassato. 
Unio lutulentus, Goutp; Proceed. Boston Soc. Nat. Hist., i. 295. 
Nov. 1850. Expedition Shells, 88. 
AnimaL having the foot slaty white, edge of the mantle and gills 
orange; siphonal fringes black; abdominal mass bright ochreous- 
yellow. 
SHELL transversely elongated, scarcely falcate, dorsal and ventral 
margins nearly parallel; posterior dorsal margin a little sloping, ends 
rounded; anterior half nearly as high as the posterior; valves rather 
solid, compressed, with a moderate constriction at the ventral margin; 
beaks at the anterior fourth, scarcely modifying the dorsal outline by 
their prominence, much eroded; surface having concentric undations 
along the posterior umbonal ridge; epidermis shining olive-green, 
pale leaf-green posteriorly, very faintly radiate-striate, and across the 
disk are some rays of distinct corrugations. Nacre bluish-white, with 
livid stains near the hinge. and a silvery brilliance posteriorly. Hinge 
with a single elongated, slightly prominent, obtuse, very oblique car- 
dinal tooth in each valve; lateral teeth slender, sharp, nearly straight, 
well developed, double in the left valve. The limbus, outside of the 
pallial impression, is much thickened. 
Length two inches; height one inch; width two-fifths of an inch. 
Inhabits New Zealand, common. Drayton. 
Resembles U. monodon, and slender specimens of U. complanatus. 
It is not a fragile shell, and the peculiar tubercular waves along its 
slope, the scattered corrugations on its disk, and its peculiar colour, 

