CHAP. X. IBIDIN^. — ANODONTIN^. 287 



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

 gin. These obviously lead io 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 Alasmodontiiv^. 



(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 a„^i„ -^r. Sub-fatnilies of 



AnodontincE. 



Analogies. Unionida. 



Anodo\. Pre-eminently typical. Unionin^. 



Symphynota. Hinge margin or tetth lamellar. Hyrian^e. 



T „„„.„„ (■ Boat-shaped, and very long, no7T„ 



Lamproscapha. < teeth j o > i Iridinan^. 



Patularia. ' Shell nearly round ; no teeth. Anodonin^. 



Vr' „^„ f Hinge plate sinuated or tubercu- 7 . , 



Hemiodon. < lated I ALASMODONiNiE. 



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. 111. pi. i. 260. 



