384 NEW EXOTIC UNIONIbiE. 



Shell smooth, subrotund, rather compressed, nearly equilateral, rounded before 

 and behind ; valves rather thick, thicker before ; beaks a little prominent, with 

 diverging undulations at the tips ; epidermis dark chestnut-brown, striate, eradiate ; 

 cardinal teeth long, compressed, oblique, crenulate and corrugate ; lateral teeth long, 

 crenulate and curved ; nacre silver-white and iridescent. 



Sab. — Amazon River, Brazil, Capt. George Brown. Rio Plata, H. Cuming. 



My cabinet. 

 Biam. 1. Length 2\3, Breadth 2-9 inches. 



Shell smooth, subrotund, rather compressed, nearly equilateral, rounded before 

 and behind ; substance of the shell rather thick, thicker before ; beaks a little pro- 

 minent, with diverging undulations at the tips ; ligament rather long and dark- 

 brown ; epidermis dark chestnut-brown, striate, without rays, with distant marks of 

 growth ; umbonial slope flattened and rounded ; posterior slope narrow, sulcate on 

 both valves ; cardinal teeth long, compressed, oblique, crenulate and corrugate ; 

 lateral teeth long, crenulate and curved, forming an arch between the cardinal and 

 lateral teeth; anterior cicatrices rather small, well impressed, confluent with the 

 lower, but distinct from the upper; posterior cicatrices rather large, confluent and 

 slightly impressed ; dorsal cicatrices placed in a row across the centre of the cavity 

 of the beaks; cavity of the shell very shallow and wide; cavity of the beaks 

 shallow and rounded ; nacre silvery white and iridescent. 



Remarks. — I have had three specimens in my collection of this species for some 

 time. It is allied to Paraneiisis, (nobis,) but may easily be distinguished by its being- 

 more lenticular or patelliform, the beaks being more medial. It is more compressed, 

 and the substance of the shell thinner. The epidermis is less shining, but like it is 

 transversely striate, being almost sulcate. The margin outside of the palleal cica- 

 trix is broad, but not so much so, nor so thick, as it is in Paranensis, nor are the 

 cardinal teeth so much divided, being disposed to be lamellar and transversely 

 striate. The circular margin and the gentle inflation from all sides towards the 

 centre of the disks, give the form of a lens to this species more nearly than any I 

 have seen. 



UNIO PERiEFORMIS. PL 43, fig. 292. 



Testa laevi, subrotunda, inflata, valde inrequilaterali, postice obtuse subangulata, antice oblique rotundata ; 

 valvulis subcrassis, antice aliquanto crassioribus ; natibus vix prominentibus, inflatis; epidermide 

 striata, nigro-virente, eradiata ; dentibus eardiualibus parviuseulis, compressis crenulatisque ; late- 

 ralibus sublougis subrectisque ; inargarita argentea et irideseente. 



Shell smooth, subrotund, inflated, very inequilateral, obtusely subangular behind, 

 obliquely rounded before ; valves somewhat thick, slightly thicker before ; beaks 

 slightly prominent and inflated ; epidermis striate, blackish green, eradiate ; cardinal 



