CHAP. X. IRIDIN^. ANODONTIN^. 287 



destitute of any crenations, or plate^ below the hinge mar- 

 gin. These obviously lead to Symphynota, where the form 

 is oval and winged ; while a slender lamellar tooth ex- 

 tends the whole length of the shell. Following this we 

 have the typical genus Anodon, where the plate in ques- 

 tion is entirely wanting. There are many striking mo- 

 dificationS;, however, in the form of these shells, which 

 may hereafter point out the sub-genera : — in Anodon 

 proper, the form is transversely oval or oblong, and the 

 bosses very small and compressed: Patularia has the um- 

 bones remarkably swollen, or ventricose ; and the shell 

 almost round : lastly, the genus Hemiodon includes those 

 which have a slight tubercle, or indication of the car- 

 dinal teeth; thus leading to the Alasmodontin^. 



(269.) Assembling these types in a tabular form, we 

 shall find they possess the usual analogies. 



Analogies of the Genera of the Anodontin^. 



Genera of the Ar,a>naiP<t Sub-families of 



Anodontince. Analogies. UnionidcE. 



Anodon-. Pre-eminently typical. Unionin^. 



Symphynota. Hinge margin or teeth lamellar. Hyrian^. 



Lamproscapha. [ ^^eeth!''^"''' ^""^ ^"""^ ^''"^ ' ""] I«i«inan^. 

 Patularia. ,' Shell nearly round ; no teeth. Anodoninje. 



Vr',...^^^»T (■ Hinge plate sinuated or tubercu-7 a. 



Hemiodon. i lated; j Alasmodonin^. 



Not having carried our analysis into the sub-genera, 

 we shall not venture to name those which have the 

 aspect of being such. It is plain, however, that there are 

 aberrant species, if not sub-genera, in Symphynota and 

 Anodon. These two are probably connected by Anodon 

 rubra, which has a distinct elevated ridge, analogous to 

 the lamellar tooth of Symphynota. The bosses, again, 

 of our common Anodon are small and compressed; while 

 those of A. trapezialis Lam., and other large species, 

 are remarkably ventricose. The Anodon purpurascens*, 



* Zool. III. pi. j. 260. 



