NEW FRESH WATER AND LAND SHELLS. 13 



posterior slope ; cardinal teeth very long, lamellar, dmMe in the right and single m 

 the left valve ; lateral teeth long, lamellar and slightly curved; anterior cicatrices 

 confluent ; posterior cicatrices confluent ; dorsal cicatrices concealed within the cavity 

 of the beaks ; cavity of the shell large, deep and rounded ; cavity of the beaks very 

 deep and rounded ; nacre bluish white and iridescent. 



Remarks. — This species has a close resemblance to U. superbus (nobis) from New 

 Holland. It may be distinguished from it by the gravidus being more inflated, by its 

 yellow epidermis and bluish white nacre. The stiperbus is a thicker shell, and the 

 teeth are less lamellar and the cardinal teeth are rather shorter. All I have seen are 

 delicately salmon colored, while the ten or twelve specimens of gravidus before me 

 are all white. The greater transverse diameter is much nearer the centre of the shell, 

 and the outline approaches more to the rotund. The three rays on the posterior slope 

 are very distinct and beautiful in the young specimens. The lunule is in several of 

 the specimens remarkably large. The cardinal teeth in right valve are disposed to 

 curve upwards. 



Mr. Haines received this species, with many interestiug ones, from Dr. House, of 

 Bangkok, Siam. 



Unio ixornatus. pi. 24, fig. 6. 



Testa laevi, elliptica, inflata, subaequilaterali, postice subangulata ; valvulis subpellucidis tenuibusque ; natibus 

 subprominentibus ; epidermide olivaceu, substriatii ; dentibus cardinalibus longis lamellatisque ; laterali- 

 bus longis, rectis lamellatisque ; margarita caeruleo-alba et iridescente. 

 Shell smooth, elliptical, inflated, nearly equilateral, subangular behind ; valves sub- 

 pellucid and thin; beaks a little prominent, epidermis olive, substriate; cardinal 

 teeth long and lamellar ; lateral teeth long, straight and lamellar ; nacre bluish white 

 and iridescent. 



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

 ^aZ..— Siam. S. R. House, M. D. 



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

 Diam. -7, Length 1, Breadth 1-8 inch. 



Shell smooth, elliptical, inflated, nearly equilateral, subangular behind ; substance 

 of the shell subpellucid and thin ; beaks a little prominent, submedial ; ligament long 

 and thin ; epidermis olive colored with minute strife and having three obscure rays 

 on the posterior slope; umbonial slope rounded; cardinal teeth long, bladed and 

 straight ; lateral teeth long, straight, bladed and very thin ; anterior cicatxices con- 

 fluent and but very slightly impressed ; posterior cicatrices scarcely perceptible ; dorsal 

 cicatrices imperceptible ; cavity of the shell deep and rounded ; cavity of the beaks 

 very small and subangular ; nacre bluish white and iridescent. 



Remarks. — Among the >*hells from Siam, submitted to me by Mr. Haines, were nine 



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