234 Mr. E, Billings on the Genus Athyris. 



objected to by several distinguished palseontologists, and in con- 

 sequence thereof abandoned by its author, yet I believe that, on 

 a careful examination of all the circumstances, it will be found 

 to be perfectly just toward the parties concerned, and in no re- 

 spect inconsistent with the rules of zoological nomenclature. It 

 was the first subdivision of the genus published, and should 

 therefore take precedence over all others. 



Previously to 1853 Athyris was only known as a single large 

 genus of Brachiopoda, which included such forms as Terehratula 

 concentrica, Von Buch, T. tumida, Dalman, and T. Herciilea, 

 Barrande. In that year Mr. Davidson divided it into two 

 smaller genera, confining the name Athyris to that section for 

 which it was most appropriate, with tumida or Herculea for the 

 type, and adopting Spirigera, D'Orbigny, for the other type, T. 

 concentrica. It was afterwards found that Athyris, as then re- 

 defined, included two genera; and in consequence it has been 

 again divided by separating all those typified by T. Herculea 

 under the name of Mei-ista, a genus proposed but not clearly 

 characterized by Prof. Suess in 1851. This is the classification 

 which 1 believe to be the true one. While discussing it I shall, 

 throughout this paper, when I may have occasion to refer to the 

 species above named, designate them Athyris tumida, Spirigera 

 concentrica, and Merista Herculea. 



Those who are opposed to this arrangement contend that, as 

 all the species which M^Coy placed in the genus at the time he 

 first described it belong to the group typified by S. concentrica, 

 the name Athyris must be retained for that group, and cannot 

 now be transferred to the other section of which A. tumida is 

 the type. This reasoning, according to my views, can only hold 

 good in case it be fii'st proved that M'Coy specially confined the 

 genus to species having the generic characters of those in his 

 original list, or pointed out one of them as the type, or drew up 

 his diagnosis in such a manner as to exclude A. tumida. In 

 this paper I shall endeavour to show — • 



1. That M'Coy did not limit his genus to the species first 

 placed in it. 



2. That, on the contrary, he and other naturalists understood 

 it to include both A. tumida and S. concentrica. 



3. That, according to the laws of zoological nomenclature, the 

 subdivision made by Davidson in 1853 cannot be set aside. 



4. That Davidson^s classification has been adopted in several 

 works, some of them of great influence and wide circulation. 



In order to prove the above propositions, I shall give the 

 more important facts of the history of the genus, with M'Coy's 

 original figure, and shall quote some of the laws above mentioned 

 in full. Much of this, of course, belongs to the common stock 



