﻿EXOTIC UNIONIDiE. 247 



lateral teeth are also thinner. In the former, the cicatrices are much more deeply 

 impressed and the nacre is of a rose color, while in the latter it is a rich salmon. In 

 neither of the specimens of these two species have I seen one with the beaks perfect 

 enough to present the important characters of them. I have no doubt they will be 

 found to differ when they shall be observed in that condition. 



Unio plicatulus. PI. 37, fig. 126. 



Testa minute plicata, valde oblonga, compressa, valde inasquilaterali, postice obtuse aogulata ; valvulis 

 tenuibus ; natibus prominulis ; epidermide luteo-fusc£i, radiate ; dentibus cardinalibus obliquis, 

 lamellatis, longis, pertenuibus, dente cardinali valvulse dextrae, duplice ; lateralibus longis, acicularis 

 rectisque ; margarita cseruleo-alba et valde iridescente. 



Shell minutely plicate, very oblong, compressed, very inequilateral, obtusely 

 angular behind ; valves thin ; beaks a little prominent ; epidermis yellowish brown 

 and radiated ; cardinal teeth oblique, lamellar, long, very thin and double in the 

 right valve ; lateral teeth long, needle-shaped and straight ; nacre bluish white and 

 very iridescent. 



Unio plicatulus, Lea. Proe. Acad. Nat. Sci., 1859, p. 152. 



Hob. — Borneo. Mr. Cuming. 



Cabinet of Mr. Cuming. 

 Diam. *5, Length -9, Breadth 1*9 inches. 



Shell with small folds, very oblong, compressed, very inequilateral, obtusely 

 angular behind ; substance of the shell thin ; beaks a little prominent ; ligament thin, 

 long and light brown ; epidermis yellowish brown, nearly covered with green rays, 

 which are more numerous and broader on the posterior half; marks of growth 

 distant ; umbonial slope slightly raised into an obtuse angle ; posterior slope com- 

 pressed, raised into a keel and covered with minute closely set folds nearly to the 

 margin ; cardinal teeth oblique, lamellar, long, very thin, double in the right and 

 single in the left valve ; lateral teeth long, needle-shaped and straight ; anterior 

 cicatrices confluent ; posterior cicatrices confluent ; dorsal cicatrix very small and 

 placed nearly in the centre of the cavity of the beaks ; cavity of the shell very 

 shallow ; cavity of the beaks very shallow and slightly angular ; nacre bluish white 

 and very iridescent. 



Remarks. — The specimen above described is the only one I have seen, and the 

 characters may be found in other and more perfect individuals to vary in some 

 degree. The beaks being eroded do not exhibit of course the character of the tips. 

 Judging from the folds, which are closely set, up to the eroded portion, I should 

 suppose that the whole region would be very beautifully covered with diminishing 

 ones to the tip. These delicate, thickly set folds are very regular and nearly parallel, 



extending not only nearly over the whole posterior slope, but round the beak and 



63 



