Remarks upon the Genus Anomahdonta, etc. 331 



Amhonycliia (^MegaptercC) Casei and AmhonycMa {Megaptcra) alata, 

 and never used or adopted the name Opisthoptera, which, in 1872, he 

 said, " if it should be thought clesirahle" he " loould propose " 



The name Opisthoptera, then, has not become a paleontological term, 

 and when it is " thought desirable" Prof. Meek may propose to use it, 

 as Meek and Worthen proposed to use Megaptero,, for shells having the 

 cardinal teeth of Amhongchia ; but he never can proi:)ose to use it for 

 shells having the cardinal tooth and hinge line of the Anomahdonta. 



In January, 1874, I made and clearly defined the genus Anomah- 

 donta, for shells having a peculiar hinge line, before wholly unknown, 

 founded upon the species A. glgantia. From part of a hinge line of A. 

 ahia, in the possession of Mr. James, I ascertained that its cardinal 

 teeth Avere not those of an AmhonycMa, but were peculiar to the 

 Anomahdonta, and, from the general shape of the shell, I then believed 

 what I am now more fully assured of, that the hinge line of the two 

 sjiecies was substantially the same, and, consequently, that i\\e Amhony- 

 cMa alata would become the Anomahdonta alata (Meek). At that 

 time, I suggested that the genus Anomahdonta would, prohably, in- 

 clude the AmhonycMa (Megaptera) Casei, hut I am now of the opinion 

 that the character of its cardinal teeth alone exclude it. I be- 

 lieve, however, with Prof. Meek, that it may become the type of a 

 new subgenus under AmhonycMa, because its lateral teeth, though 

 unknown, are probably different from the true AmhonycMa. I do not, 

 however, from the statement of Prof. Meek, think that it can wear the 

 name Megaptera according to the rules of nomenclature, nor the name 

 Opisthoptera, until actually proposed and used by somebody. 



As to 3Iegaptera, it having been previously used for a genus of 

 Avhales, it can not be used for the generic name of shells, under the 

 tenth rule of the British Association for the Advancement of Science, 

 which is now a law to all naturalists ; this rule and the reasons for its 

 adoption are as follows : 



"It being essential to the binomial method to indicate objects in 

 natural history by means of two words only, without the aid of any 

 further designation, it follows that a generic name should only have 

 one meaning ; in other words, that two genera should never bear the 

 same name. For a similar reason, no two species in the same genus 

 should bear the same name. When these cases occur, the latter of the 

 two duplicate names should be canceled, and a new term, or the 

 earliest synonym, if there be any, substituted ; when it is necessary to 

 form new words for this purpose, it is desirable to make them bear some 

 analogy to those which they are destined to supersede, as Avhere the 

 genus of birds, Pleciorhynchus, being preoccupied in ichthyology, is 



