300 Journal of concmology, vol. ii, no. id, April, 1906. 



assuming that Lophocercns and Placobranchus are developed from 

 similar larvae, one of which develops as a Tectibranch, preserving its 

 shell, and the other as a Nudibranch, breaking its shell, does it fol- 

 low that for systematic purposes the two forms should be separated 

 from the Tectibranchs and Nudibranchs respectively and united in 

 one group ? 



Lophocercus. 



This genus has usually been called Lophocercus by those who have 

 treated of it separately (Krohn, Souleyet, Bergh, etc.), but Oxynoe by 

 the authors of general works on conchology and malacology (Pilsbry, 

 Fischer). It would seem that the former name is entitled to priority, 

 and that the title Oxynoe Rafinesque, 1819, is really misleading, inas- 

 much as the name cannot be shown to have been applied to this 

 animal before 1863. 



Rafinesque^ describes it thus: — "Oxynoe (mollusque) corps rampant 

 a grande coquille dorsale exterieure, bulliforme, a spire simple, ventre 

 ou pied etroit a branchies marginales striees transversalement, man- 

 teau elargi en deux ailes laterales, deux tentacules non retractiles. 

 Different du genre Sigaretus par sa coquille ext(^rieure, etc." This 

 description is not only inadequate, but it is impossible to say with 

 certainty that it is an attempt to describe Lophocercus, since no 

 notice is taken of the most characteristic external feature — the long 

 tail. The older malacologists merely reproduce Rafinesque's name 

 without giving any further description, but in 1863 Morch described 

 under the name of Oxynoe antUlarum an animal undoubtedly belong- 

 ing to the genus under consideration ; and as this was the first 

 definition of what is really meant by Oxynoe, the use of the name 

 must be considered to date from that year, and not from 18 19. But 

 in 1847 Krohn gave a full description of the Mediterranean species, 

 under the name oi Lophocercus sieboldi, which, therefore, seems entitled 

 to priority. 



Forbes^ says : — " The animal for which I propose to constitute the 

 genus Icarus, differs from Aplysia in having but two tentacula and in 

 being prolonged posteriorly into a slender lanceolate tail. The dorsal 

 shield resembles the shell of a Bullsea." This description is recog- 

 nizable, though not full, and if the law of priority is strictly applied, 

 the genus should be called Lcarus ; but nothing would be gained by 

 reviving a name which appears not to have been used by any other 

 writer. 



Lophocercus is evidently closely allied to Lobiger, but is distin- 

 guished by its narrow foot, long tail, more distinctly bulloid shell, 



1 Journal de Pkysii/uc, vol. 89, i8ig, p. 152. 



2 " Report on Moll, and Rad. of .■\egeaii," 184^, )). 1S7. 



