﻿EXOTIC UNIONIDiE. 243 



nent, corrugated and folded at the apex; ligament long, narrow and light brown; 

 epidermis very dark olive, shining, obscurely rayed on the side, but furnished on each 

 side of the posterior slope, with three well marked rays from the beak to the posterior 

 margin; umbonial slope raised into an obtuse angle; cardinal teeth rather small, 

 compressed, crenulate, straight and double in both valves; lateral teeth very long, 

 lamellar and straight ; anterior cicatrices distinct and well impressed ; posterior 

 cicatrices confluent ; pallial cicatrix well impressed ; dorsal cicatrices situated on the 

 under side of the plate within the cavity of the beaks ; cavity of the shell deep 

 and wide ; cavity of the beaks deep and subangular ; nacre silver white and very 

 iridescent. 



Remarks. — A single specimen only has been submitted to me by Mr. Cuming. It 

 is nearest in outline and general appearance to IT. saggittarius (nobis) from Siam, but 

 is a larger species, more regularly cylindrical, darker epidermis and with thicker 

 teeth. It is somewhat like U. Murchisonianus (nobis), but has no folds, is wider and 

 not so much compressed. It has also some resemblance to U. Dnnkerianus (nobis) in 

 color, polish and outline, but it has no folds, is not so much compressed and has not 

 an elevated carina. The teeth are very well defined in Shanghaiensis, and in the 

 right valve the lateral tooth is disposed to be double in this specimen, which may 

 not, however, be universally the case. It is very unusual in any Unio to have double 

 lateral teeth in both valves. 



Unio Layardii. PL 36, fig. 122. 



Testa laevi, elliptica, inflata, postice obtuse angulata, antice regulariter rotunda tti, subaequilaterali ; valvulis 

 crassiusculis ; natibus prominulis ; epidermide valde polita, micante, tenebroso-fusca, nigricante, 

 eradiata ; dentibus cardinalibus longis, lamellatis, obliquis, in valvulam dextraui duplicibus; lateralibus 

 lorigis subcurvisque ; margarita alba et iridescente. 



Shell smooth, elliptical, inflated, obtusely angular behind, regularly rounded before, 

 nearly equilateral ; valves a little thickened ; beaks a little prominent ; epidermis 

 much polished, bright, very dark brown, passing into black, without rays ; cardinal 

 teeth long, lamellar, oblique, double in the right valve; lateral teeth long and some- 

 what curved ; nacre white and iridescent. 



Unio Layardii, Lea. Proc. Acad. Nat. Sci., 1859, p. 153. 



Hob. — Ceylon. Frederick Layard. 



Cabinet of Mr. Cuming, London, and C. M. Wheatley, Phoenixville, Pa. 

 Diam. 12, Length 1*8, Breadth 2-8 inches. 



Shell smooth, elliptical, inflated, obtusely angular behind, regularly rounded before, 

 nearly equilateral and slightly curved on the dorsal line ; substance of the shell 

 moderately thick ; beaks a little prominent, submedial ; ligament slender, cinnamon 

 color ; epidermis very smooth, polished, bright, without rays, very dark brown, 



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