INYEKTKI'.KATK PALEONTOLOGY. 31 



genus Pteria (= Avlcula). Such a rule, however, it" consistently carried out 

 in the classification of the whole animal kingdom, including all of the extinct 

 and living forms, would result in the complete obliteration of most, if not all, 

 generic distinctions. 



The genus Pteria dates back to Palaeozoic times ; though most of the 

 older Palaeozoic species referred to it under the name Avlcula belong to the 

 genera Pterinea, Aviculopecten, and perhaps, in part, to a number of undefined 

 genera. There certainly are, however, true typical species of this genus in the 

 Palaeozoic rocks Pteria longa (— GervlUla longa, Geinitz), from the Carbon- 

 iferous rocks of the Western States, I have ascertained, has exactly both the 

 internal and external characters of this genus. This group also ranges 

 through all of the later formations, and is well represented in the seas of the 

 present epoch, in which latter it probably attains about its greatest numerical 

 development. The recent species belong both to the typical and Electro-ma 

 sections; while Oxytoma seems to be mainly confined to the Jurassic and 

 Cretaceous rocks, with possibly the exception of a few Upper Triassic 

 species. Pseudoptera seems to be exclusively Cretaceous. 



In regard to the name that should be retained for this genus, somewhat 

 different opinions are entertained. Klein's name Avlcula has long been in 

 use, and is adopted by most authors. As Klein, however, neither in practice 

 nor date, can be ranked as a binomial author, his names ought not to be 

 adopted, excepting where they have been fixed in zoological nomenclature, 

 by being adopted by some regular authority, previous to the application of 

 any other names to the same groups by some regular binomial naturalist. 

 So far as I am aware, however, the name Avlcula was not adopted in accord- 

 ance with the binomial system previous to the publication of the name Pteria 

 by Scopoli in 1777. As the latter author dates after the introduction of the 

 binomial nomenclature, with which he strictly conformed, and his type was 

 Mytilus hirundo, regarded by all as the type of Avlcula, the two names 

 Pteria and Avlcula are exactly equivalent. Consecpiently, I do not see 

 how we are to avoid adopting the former if we are to follow the gen- 

 erally-admitted rules of nomenclature, as was shown by Dr. Gray long back. 

 If we can disregard the rules in one case, of course we may in others, and 

 the consequences would be that every author could follow his own rule; 

 which would, of course, be equivalent to no rules at all, to the great confusion 

 of all natural-history nomenclature. 



