282 NEW U,NIONID^, MELANID^, ETC., 



teeth somewhat thick, short, compressed, crenulate, double in both valves ; lateral 

 teeth rather long, nearly straight and lamellar; nacre white and very iridescent, 

 Proc. Acad. Nat. Sci. 1866, p. 133. 



Hah. — Siam, Thomas R. Ingalls, M.D. 



My cabinet. 



Diam. -5, Length -8, Breadth 1-4 inch. 



Shell smooth, elliptical, very inequilateral, obtusely angular behind, rounded 

 before; substance of the shell somewhat thick, thicker before; beaks rather 

 prominent, minutely undulate at the tips ; ligament short, thin and light brown ; 

 epidermis yellowish-green, green prevailing on the poKSterior half, shining, obscurely 

 rayed, with broad distant marks of growth ; umbonial slope obtusely angular and 

 somewhat raised; posterior slope narrow elliptical, with two green rays on each 

 valve ; cardinal teeth somewhat thick, short, compressed, crenulate, double in both 

 valves ; lateral teeth rather long, nearly straight, lamellar, disposed to be treble in 

 both valves ; anterior cicatrices distinct, large and well impressed ; posterior 

 cicatrices confluent, slightly impressed and large ; dorsal cicatrices placed above 

 the centre of the cavity of the beaks ; cavity of the shell rather deep and wide ; 

 cavity of the beaks rather deep and angular; nacre pearly-white and very iridescent. 



Remarlis. — A single specimen only was received from the late Dr. Ingalls. In 

 outline it is near to caeruleus (nobis), but differs in being a smaller and thicker 

 species, as well as in having a smoother and greener epidermis. The cardinal teeth 

 are also thicker and shorter. In the lateral teeth they are entirely different, the 

 specimen before me having three nearly perfect ones in both valves. Whether this 

 be a constant character can only be proved by the examination of other specimens. 

 This specimen came with asperulus, herein described, and is about the size and has 

 somewhat the same appearance; but that shell is more elliptical, has lamellar 

 cardinal teeth, and is furnished with obscure folds, while pilatus is perfectly smooth. 

 The tips of the beaks of this specimen are eroded, but the small closely-placed folds 

 are visible all around the eroded parts, and indicate that they commenced at the very 

 point. 



TJnio eufofuscus. pi, 39, fig, 96. 



Testa plicata, subqoadrata, subsulcata, sublenticulari, insequilaterali, postice rotundata, antice 

 rotunda ; valvulis crassiusculis, antice crassioribus ; natibus prominulis, crebre et minute 

 plicatis; epidermide rufo-fusca, eradiata, micanti ; dentibus cardinalibus subcompressis, obliquis, 

 crenulatis, in utroque valvule subduplicibus ; lateralibus longis subcurvisque ; margarita alba et 

 iridescente. 



Shell plicate, subquadrate, slightly sulcate, sublenticular, inequilateral, rounded 

 behind and round before ; valves somewhat thick, thicker before ; beaks slightly 



