CHAP. X. IBIDIN^E. - ANOBONTIN.E. 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^E. 



(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 ,. .. Sub-families of 



Anodontince. Analogies. Unionid*. 



ANODON. Pre-eminently typical. UNIONIN^E. 



SYMPHYNOTA. Hinge margin or teeth lamellar. HYRIAN.E. 



LAMPROSCAPHA. te - th ' and ** lon S ' no ] 



PATULARIA. ~ Shell nearly round ; no teeth. ANODONINJB. 



HEMIODON. { *g* sinuated or tubercu ' } 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. i. 260. 



