﻿AND SPECIES OF THE FAMILY UNIONID^. 295 



valves very thin ; beaks slightly prominent ; epidermis greenish yellow, obsoletely 

 radiated ; cardinal teeth lamellar and thin ; lateral teeth long, lamellar and slightly 

 curved ; nacre bluish white and iridescent. 

 Proc. Acad. Nat. Sci. Vol. 8, p. 93. 

 Hob.— Siam. S. R. House, M. D. 



My cabinet and cabinet of W. A. Haines, New York. 

 Diam. -5, Length 1-6, Breadth 2 inches. 



Shell winged, with numerous small folds over the beaks and posterior slope, obovate, 

 compressed, very inequilateral, rounded and compressed behind ; substance of the shell 

 very thin and delicate : beaks slightly prominent and minutely undulate ; ligament 

 long and very thin ; epidermis greenish yellow with three very distinct rays over the 

 posterior slope ; cardinal teeth lamellar, double in the right and single in the left valve : 

 lateral teeth long, lamellar and slightly curved, treble in the left and double in the 

 right valve ; anterior cicatrices confluent and slightly impressed ; posterior cicatrices 

 apparently none ; dorsal cicatrices placed in the centre of the beaks ; cavity of the shell 

 very shallow ; cavity of the beaks shallow, angular ; nacre bluish white and iridescent. 

 Remarks. — In outline and general appearance this interesting species resembles the 

 young of Unio alatus, Say. It may at once be recognised to be different by the numerous 

 small folds — which are visible in the interior as well as the exterior — as well also by 

 the peculiar number and place of the lateral and cardinal teeth. It would naturally 

 follow, as a plicate shell, U. Nkldinianus, (nobis.) The most remarkable feature 

 in this species is the possession of three lateral teeth in the left valve. In the eight 

 specimens before me the three teeth are recognised. In all of them the upper division 

 is smaller than the two lower ones, and the upper one of the two of the right valve is 

 also always smaller. The cardinal teeth are remarkable for being double in the right 

 and single in the left valve. Some of the specimeus are enlarged over the umbonial 

 slope, immediately behind which there is a slight emargination at base. The enlarge- 

 ment is owing probably to sexual difference. 



Unio tumidulus. PI. 25, fig. 9. 



Testa lsevi, obliqua, inflata, postice 'angulata, valde inaequilaterali ; valvulis suberassis; natibus prominenti- 

 bus ; epiderrnide tenebroso-olivacea, striata ; dentibus cardinalibus longis larnellatisque ; lateralibus 

 pralongis subcurvisque ; margarita alba et iridescente. 

 Shell smooth, oblique, inflated, angular behind, very inequilateral ; valves rather 

 thick ; beaks prominent ; epidermis dark olive, striate ; cardinal teeth long and lamel- 

 lar ; lateral teeth very long and somewhat curved ; nacre white and iridescent. 

 Proc. Acad. Nat. Sci. Vol. 8, p. 93. 

 Hob.— Siam. S. R. House, M. D. 



My cabinet and cabinet of W. A. Haines, New York. 

 Diam. -8, Length l-l r Breadth 2 inches. 



