1895.] NATURAL SCIENCES OF PHILADELPHIA. 347 



ON THE STATUS OF THE NAMES APLYSIA AND TETHYS. 

 BY HENRY A PILSBRY. 



In the course of my studies on the " Sea Hares," preliminary to 

 the preparation of a monograph of this group of Teotibranch Mol- 

 lusks for the Manual of Conchology, my attention was early forced 

 to the fact that in Linnaeus' Tenth Edition of the Systema Naturae 

 the genus Tethys was proposed for the animal now known as Aphjsia, 

 and included nothing else. Moreover, by the terms of the generic 

 diagnosis, such creatures as that known as Tethys in modern times 

 are excluded. 



In the Twelfth Edition of the Systema, Tethys is given a completely 

 different meaning ; and the new term Aphjsia ( Laplysia) is brought 

 forward to include the species of tbe earlier Tethys. This later- 

 usage has been accepted by zoologists until the present day. 



The question then arises, shall we apply to Linnaeus himself the 

 canons of nomenclature which would be rigorously enforced were 

 the claims of his successors in question ? It is with a view to obtain- 

 ing the opinions of those who are expert in these matters that we 

 present below a full synopsis of the literature bearing upon the 

 questions at issue. 



The facts in this case have doubtless been fully unearthed by 

 many investigators; but probably believing it best to " let sleeping 

 dogs rest" no one 1 has to my knowledge seriously raised the ques- 

 tions to which I desire now to direct attention. 



The genus Tethys was founded by Linne in the tenth edition of the 

 Systema Naturae, p. 653, for two species, thus: 



" 254. Tethys. I 'orpus oblougum, bilabiarum : corpusculo 

 medio cartilagineo oblougo. Tentacula duo, cuneiforma. Foramina 

 duo, spirantia. 

 " limacina 1. T. auriculis quatuor. 



Habitat in Oceano Aastrali. 



1 ExceptE. Leigh, who in Mai. Unters. I. p. 33, in Semper's Keisen, 2ter Theil, 

 has made the bald statement that Linnaeus' earlier Tethys was an Aplysia, but 

 who continues to use Tethys for the Nudibranch. 



