GENUS ATIIYRIS. 261 



This I suppose we may consider as " unsophisticated" reasoning in 

 relation to the subject. It amounts to this : ' Prof. M'CoY had in his mind 



* the imperforate A. tumida as the type of his genus'; but being engaged in 

 ' describing carboniferous fossils, he did not mention it, and followed his 

 'generic description with A. concentrica, etc., which species he says he had 



* seen with imperforate beak.' 



We think Prof. M'Coy did just what other naturalists would have done 

 under similar circumstances. Seeing the necessity of a separation of these 

 forms from Terebratula, he proposed the obvious characters on which the 

 distinction was founded. The question of perforate or imperforate beaks, 

 in this group of fossils, may be open to discussion; at least in all that I 

 have examined, I have found no entire beaks ; but in some of the gibbous 

 forms, the apex is so incurved as to give an "apparently imperforate" 

 character, and the species are thus cited. In some species tliis perforation 

 is well defined by deltidial plates below ; but generally these are absent, 

 and the upper side of the foramen presents a semicircular outline, com- 

 municating with a triangular space which at some period has been 

 occupied by the deltidial plates. After a careful examination of hundreds 

 of specimens, I am compelled to conclude that this feature, or its modifica- 

 tion, is not reliable for specific distinctions, and certainly not of generic 

 importance, 



Mr. Billings, after citing the list of species placed under the G-enus 

 Syirigera by M. D'Orbigny, remarks as follows: 



" Several of the above species do not belong to the group. This list shows that 

 D'Orbigny regarded the genus as including not only the types of Athyris and 

 Spirigera, but also that of the Genus Merista (M. herculea) , which I shall notice 

 farther on. I think it quite certain that had D'Orbigny been aware that the genus 

 was capable of subdivision, he would have retained Athyris for one of the groups 

 which have the beak imperforate. Indeed, according to^he laws of nomenclature, he 

 could not have done otherwise with any probability of producing a permanent clas- 

 sification." 



I ca^ agree entirely with Mr. Billings, that had D'Orbigny known 

 of any group of these fossils with imperforate beaks, he might have retained 

 for it the name Athyris ; or, had he known all that has since been learned, 

 he would have made some modification in his generic terms. 



On the sixth page of his article, Mr. B. cites M'Coy's re-descriptions of 

 the genus Athyris in 1852, when, for the first time, he placed A. tumida 

 under it ; forgetting, however, to allude to the fact already stated, that 

 M'CoY there cites Spirigera as a synonym of Athyris. According to the 

 reasoning of Mr. Billings, and to reach the object he desires, we are to 

 wait from 1844 to 1852 f r Prof. M'Coy to complete his generic descrip- 

 tion of Athyris., and place under it a typical species of the genus. Suppose, 

 in the meantime, some one had based a Genus Billingsia on the Terehratula 

 tumida, would the original description of M'CoY have covered that too ? 



I will quote here the following paragraph of Mr. BiLLlNGS, from page 

 54 of the Am. Jour, of Science : 



