272 NEW UNIONIDiE, MELANIDiE, ETC., 



curved ; anterior cicatrices confluent and deeply impressed ; posterior cicatrices con- 

 fluent, large and slightly impressed ; dorsal cicatrices placed in the centre of the 

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

 shallow and rounded; nacre silver-white and beautifully iridescent. 



Remurhs. — A single specimen only was received. The elliptical outline of this 

 species is very perfect, exhibiting great regularity. In this character it closely re- 

 sembles regularis (nobis), but in the form of the teeth and in its inflation it is totally 

 different. It is most nearly allied, of all tlie South American species with which I 

 am acquainted, to piceus andi lepidus (nobis), but cannot be confounded with either, 

 being a larger and wider species, and being elliptical in outline. The disposition to be 

 treble in the left valve may be only occasionally so. In this specimen it is separate 

 from the two larger divisions below. The specimen is too much eroded at the beaks 

 to exhibit the usual divergent character of the folds of the tips, and the epidermis is 

 so much removed that the description of it is necessarily very imperfect. 



MONOCONDTLCEA LENTIFORMIS. PI. oG, fig. 86. 



Testa Ijevi, rotundata, lenticulari, valde inasquilaterali, postice rotundata, antice curta rotundaque ; 

 valvulis subcrassis, antice erassioribus ; natibus proruinentibus, ad apices acuminatis, retusis ; 

 epidermide tenebroso-oliva, striata, radiata; dentlbus cardinalibus parviusculis, tuberculatis ; 

 margarita albida et valde iridesceute. 



Shell smooth, rounded, lenticular, very inequilateral, rounded behind, short and 

 round before ; valves rather thick, thicker before ; beaks prominent, acuminate at 

 the tips, retuse ; epidermis dark olive, striate and eradiate ; cardinal teeth rather 

 small, tuberculate ; nacre whitish and very iridescent. 

 Proc. Acad. Nat. Sci. 1866, p. 34. 



Eab. — South America, Don Patricio M. Paz. 



My cabinet and cabinet of Don P. M. Paz. 

 Diam. -7, Length TS, Breadth 1-6 inch. 



Shell smooth, rounded, lenticular, A^ery inequilateral, rounded behind, short and 

 round before; substance of the shell rather thick, thicker before and near the basal 

 margin ; beaks prominent, acuminate at the tips and retuse ; ligament small and 

 very dark brown, almost concealed ; epidermis dark olive, striate and without rays ; 

 umbonial slope flattened ; posterior slope narrow elliptical, carinate, with two green- 

 ish lines on each valve from the tips to the posterior margin ; cardinal teeth rather 

 small, tuberculate and somewhat erect; anterior cicatrices confluent, large and 

 moderately well impressed; posterior cicatrices confluent, large and very slightly 

 impressed; dorsal cicatrices concealed in the cavity of the beaks; cavity of the shell 

 shallow and wide; cavity of the beaks shallow and angular; nacre whitish, tinted 

 with salmon and very iridescent. 



