CHAP. X. 



ALASMODONTIN^. 



289 



arrangement. The ex- 

 ceedingly oblique teeth 

 of our Uniopsis radiata* 

 (Jig. 62.) show it is the 

 prototype of Unio, and 

 might have been there 

 placed, but for the want 

 of lateral teeth. The 

 triangular and cuneated 

 shape of Alasmodon un. 

 dulata reminds us of 

 ^glia. The single cardinal tooth of Calceola t7'uncataf 

 accords with the tubercles of Hemiodon; while the 

 compressed bosses and dilated posterior side of Compla- 

 naria preserves the analogy between this sub-genus and 

 its prototypes Lymnadia, T^heliderma, and Anodon. 

 Finally, we come to Margaritana, which, every one 

 must perceive, puts on the aspect of Mysca, Ligumia, 

 Potomida, and the Iridince. Wliether the whole of 

 the shells retained by us in this last genus really enter 

 into the circle we are at present tracing, or that such 

 as have an obsolete lateral tooth should naturally be 

 arranged with the Potomida Uttoralis^ &c., cannot, of 

 course, be yet determined ; nor do we feel certain that 

 Calceola is the connecting type with the AnodontincB. 

 And yet, as all these find their representatives in the lead- 

 ing divisions of the Unionid^, they become absolutely 

 types of genera, equivalent in rank, although not in 

 numbers, to the genera of the sub-family Unionin^. 

 This will be further apparent from the following expo- 

 sition : — 



* I suppose, from the name, that this is the Margaritana radiata of 

 Lea's Synopsis, but, as no reference is made to where the shell is described, 

 or any information beyond its being " non-symphynote and smooth," I 

 affix this name at a venture, merely for my present purpose; the real name, 

 if described, can always be made out from the figure here given. Since 

 writing the above, my kind friend Mrs. Corrie (who has a noble series of 

 Unionidce in her fine collection) has sent me a specimen of this type under 

 the name of Alasmodon inflata ; the teeth are not near so oblique as in that 

 here figured. 



t Under the common name of XJnio calciolus, we have received three 

 distinct species from America. 



U 



