494 Zoological Society. in this character : it is rounded anteriorly, and is subangular pos-teriorly. The dorsal margin is nearly straight, the basal margin is slightly emarginate, the disc being disposed to be flattish. In the specimens under examination, the beaks are all more or less eroded, but in the youngest there are slight indications of undulations. The liga-ment is thin and long ; the marks of growth are distant and rather dark, and the epidermis in the young is yellow or greenish, in the older it is darker and brown ; the anterior cicatrices are distinct ; the dorsal small, and placed in the cavity of the beaks. The five species herein described are remarkable in the character of the dorsal line, which rises immediately under the margin into a dentoid line, somewhat lamellar, and approaching in its character the more distinct tooth of the genus Dijjsas (Leach). In the younger specimens this is much more distinctly marked, and in the older it becomes obsolete. This group of Anodontfe, having this dentoid character, woxdd seem to form a natural connexion on one side with the genus Dipsas, and on the other with the genus Unio, connecting with U. Bengalensis, brought by Dr. Burrough from India, and described by me in the 'Trans. Am. Phil. Soc' aoI. vi. pi. 2. fig. 3. This peculiar form of tooth, if it may so be called, is peculiar to that part of the world, so far as my observation extends ; for among the numerous species examined by me from Europe, Africa and America, South as well as North, I have never met with this character deve-loped as in those alluded to above. Anodonta crepera. a. testd eUi])ticn, subcompressii, i7icequi-latei'ali ; valvuUs temdhus ; natibus subprominentibus ; epider-mide tenebroso-fuscd ; margaritd vel alba vet purpured. Hub. Bongabon, Luzon, Philippines. Diam. 1-1 ; length TS ; breadth 3'3 inches. Remarks. — Five of the six specimens under examination are purple, the sixth whitish. The outline is nearly oval. One of the specimens is obtusely biangular posteriorly ; the substance of the sh^ll is slightly thickened anteriorly ; the beaks are too much eroded to observe any undulations ; the ligament is rather short and thin ; anterior cica-trices distinct ; dorsal cicatrices small, and placed in the centre of the cavity of the beaks. The species is closely allied to A. tenuis, but is not quite so thin and is more transverse. Three specimens of the young have a well-defined anterior lamellar tooth and a distinct pos-terior raised line, which in the left valve is slightl}^ divided. This is so marked in these young specimens, that one would scarcely hesitate to place them among the Uniones if we had not the adult, which have scarcely a vestige of the elevation on the dorsal line. Anodonta tenuis. A. testd ellipticd, compressd, ineBquilate-rali ; vahulis pertenuibus ; natibus subprominentibus ; epider-mide tenebroso-fuscd. Hab. Sual, Luzon, Philippines. Diam. 1 ; length \'7 ; breadth 3 inches. Remarks. — This is very closely allied to An. crepera herein de-scribed, and may, perhaps, when more specimens of the old and young
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