OF CONCHOLOGY. 121 



the list of genera, (wliich we have quoted,) but apparently in 

 the order of their publication. 



The sequence of genera in the foregoing examples, can cer- 

 tainly be much improved ; lo may be considered as the highest 

 development of the canaliculate shell, and is also the largest 

 in size ; we find, moreover, as Mr. Lea has justly remarked, 

 the most ponderous species aniong the TrypanostomcC (Pleuro- 

 cene.) I would then commence with /o, and proceed thus : — 

 lo, Pleurocera, Angitrema, Lithasia, Strephobasis, Euryaxlon, 

 Goniobasis, Schizostoma, 3fesechiza, Anculosa. 



AVe thus proceed from a long canaliculate aperture to one 

 in which the aperture is entire, we also commence with the 

 largest and close with the smallest species. Pachycheilii.s is 

 not included in the above, because it represents an extra limi- 

 tal group, and will probably be found to belong to another 

 family, or subfamily. The same may be said of Hemisinus 

 and Paludomus. 



With regard to nomenclature, we will examine — 



1. lo, Lea. — We find this genus universally recognised. 

 European authors, however, do not seem to understand its true 

 limits, and include species of Lithasia. 



2. Pleurocera, Eaf. — Notwithstanding Mr. Lea's assertion 

 that Swainson's figure of Ceriphasia sulcata does not represent 

 a species of this genus, nor his description correspond to it, 

 I believe that Ceriphasia was certainly intended for that group 

 of Trypanostomoid shells represented by canaliculaia, Say, and 

 that the figure represents some such shell as T. m.ori/orme^ Lea. 

 Gray also, in 1847, proposed Telescopella for Melania undulaia, 

 Say, which belongs to the same group. 



Thus, Mr. Lea's Trypanostoma is unquestionably a synonym. 



Pleurocera, Rafinesque, is the same shell, and having pri- 

 ority over all the other names ; I adopt it without hesitation. 



/Strepoma, Raf. MSS. applies to the same genus, and 

 Oxytrema, Raf. (Jour, de Physique,) may be intended for some 

 immature form of canaliculata, or its allies, Avhich possesses the 

 sharp-pointed aperture described, — as lo variabilis, Lea, for 

 instance. 



Messrs. Adams adopt Ceriphasia, but they separate certain 

 species, reticulate, or nodulosely carinate in the middle, to 

 form their genus Elimia. Thair Megara, also, consists of 

 species of this genus. 



Of course these names are not founded on generic characters, 

 and, at best, can only be used to designate groups. 



3. Lithasia, Haldeman. — This genus is recognized by Messrs. 

 Adams, but Mr. Reeve and Dr. Brot confound its species with 

 lo. Prof. Haldeman first proposed it as a subgenus of 

 Anculosa. " Shell heavy, having protuberances." This char- 



