a Genus of Frcsh-licatcr Bivalve Shells, •^r. 1 1 j 



try. Judging ft-om the figui'e, the breadth of the shell is 

 rather more than six inches ; its length, irom the umbones to 

 the basal margin, two and a quarter ; and at the anterior end 

 two and a halt : from the umbones diverge two sets of radiat- 

 ing striag crossing both the extremities ; but whether these 

 striae are elevated or depressed is uncertain ; tiie basal mai'giu 

 is sinuated, or gradually contracted, in the middle. 



The specific name of exotica, given by Lamarck to this 

 species, being applicable to all that are known, I have pro- 

 posed that oi' striata as descriptive of its peculiar character. 



2. Iridina elongata. 



I. testa leevi, transversim oblonga, antice lata ; margine 

 basali integro ; umbonibus subretusis. 



Shell smooth, transversely oblong, anteriorly broad ; basal 

 margin entire; umbones subretuse. — /. elongata. Soiverbi/s 

 Genera. 



Not having myself examined this shell, I can only judge of 

 its characters Irom tlie figure given by Mr. Sowerby, and 

 to which no description is subjoined. It appears perfectly 

 smooth, of a greenish olive colour, and the umbones less pro- 

 minent than the last: the basal margin also is not sinuated; 

 and the size somev/hat smaller. This shell is now in the pos- 

 session of the Rev. Dr. Goodall. 



3. Iridina ovata. 



I. testa la?vi, transversim ovata ; umbonibus prominentibus, 

 vix mediis. 



Sliell smooth, transversely oval; umbones prominent and 

 neaily medial. 



One perfect valve of this excessively rare shell lias recently 

 come to my hands, and is I'emarkably distinct from the two pre- 

 ceding. Its form is short and oval ; the umbones very pro- 

 minent, and nearly placed on the middle of the hinge mar- 

 gin. The colour dark-brown tinged with greenish, and en- 

 tirely smooth. 



Tiiere is one valve of a species belonging to this genus in 

 the British Museum ; it is polished, and the margin appears to 

 have been cut; the name attached to it is Iridina exotica; 

 that it is not the Iridina exotica of Lamarck, is too obvious 

 to require argument. If" it be a valve of any of the s^jecics 

 Ijcre enumerated, it most {irobably is one belonging to tlie 

 species hist descril)ed; but, I'rom its imperfect state, the ques- 

 tion cannot positively be decided. 



Vol. GL No. 298. I'«h. 182,'}. P XXVII. lie- 



