430 MOLLUSCA. 
Inhabits Hunter’s River, New South Wales. 
Slender varieties have much the appearance of the more expanded 
forms of U. lutulentus. It is more tumid, the beaks more elevated and 
more central, the entire dorsal margin less direct, the hinge more 
curved, the cardinal tooth of the right valve more oblique and distinetly 
bifid, the lateral tooth of the left valve less extensively cleft, and I can- 
not find that it is ever nodular along the posterior slope. ‘The nacre 
has a tendency to salmon-colour, and it does not seem to accumulate 
a dense coating of mud externally. Its exterior is almost precisely 
like Anod. areolata. 
Figures 543, 543 a, 543 }, three views of the shell. 
Unio porsuosus (Gould). 
T. transversa, retrorsum ampliata, inequilateralis, compressa, castanea ; 
latere antico circulari ; latere postico oblique rotundato ; margine dor- 
sali recto ; apicibus pro-eminentibus, antrorsum concentrice costato- 
undulatis, retrorsum nodoso-fluctuatis: dente cardinal perobliquo, 
elongato, compresso ; dente lateral recto: margarita ex albo-cerules- 
cens, livido ad umbones tincta. 
Unio dorsuosus, Goutp; Proceed. Boston Soc. Nat. Hist., in. 296. 
Nov. 1850. Eixpedition Shells, 89. 
SHELL transversely oblong-ovate, thin, rather compressed, chestnut- 
brown; beaks prominent, radiately plicate in front by four or five 
delicate concentric ribs; nodose-fluctuate along the posterior umbonal 
slope; remainder of the surface smooth; posterior half one-third 
broader than the anterior; dorsal margin rectilinear, posteriorly com- 
pressed and obliquely rounded at the extremity; anterior tip semi- 
circular. Cardinal teeth lamellar, delicate, slightly oblique; lateral 
teeth straight, short, and delicate. Nacre bluish-silvery, opaque white 
at the posterior ventral region. Cavity of the beaks deep, tinged with 
rusty greenish. Anterior cicatrix well impressed; posterior cicatrix 
scarcely perceptible; anterior ventral margin thickened. 
Length an inch and a half; height seven-eighths of an inch; breadth 
half an inch. 

