APPENDIX A. 



DESCRIPTION of Sylon challengeri, n. sp., a Parasitic Cirriped. By Dr. P. P. C. 

 Hoek, Member of the Royal Academy of Sciences of the Netherlands. 



In' May 1886 Mr. C. Spence Bate sent me a specimen that looked like a Sacculina, 

 the only one that he ever saw of the kind attached to a Macrurous Crustacean. 



The Macruran. to which it was attached was a specimen of Spirontocaris spinus 

 (Sowerby), var e. It was taken during the voyage of the Challenger at Station 49, off 

 Halifax. It is figured on PI. CVI. fig. 5e, of Mr. Spence Bate's Report, being shown 

 in situ ; in fig. 10 of the same plate it is shown isolated. In the explanation of this 

 plate it is referred to as a saccular parasite. 



At the suggestion of Mr. Spence Bate, Mr. John Murray, Director of the Challenger 

 Commission, asked me to describe the specimen in order to have a description of it 

 embodied in Mr. Spence Bate's Report, a recmest which I gladly accepted. 



The reason Mr. Bate proposed to send the parasite in question to me, was that he 

 believed it to be a parasitical Cirriped. After careful examination, I am able to confirm 

 Mr. Spence Bate's provisional determination ; for I found that it belonged to a genus of 

 the Rhizocephala, or parasitical Cirripedia, Sylon, a genus well known to the Norwegian 

 zoologists, but no specimens of it had been previously taken in the Atlantic south of 

 lat. 60° N. 



Before proceeding to describe the specimen, it will be well to say something con- 

 cerning: the literature of the genus. 



In 1855 H. Kroyer 1 published a short note on a very insufficiently known group of 

 ( 'rustaceans, Pachybdella and its congeners. This note is remarkable from a historical 

 point of view, since for the first time a third genus of these lower Crustaceans, which 

 afterwards were shown to form the group of the Rhizocephala, was spoken of. The two 

 previously known genera are Pachybdella, Diesing (Saccrdina, Thompson), and Pelto- 

 gaster, Rathke. Of Pachybdella, the species of which inhabit Crabs, Kroyer mentions 

 two species, and of Peltogaster, which occurs on the abdomen of Pagurus, five different 



1 H. Kroyer, Bemaerkninger om en meget ufuldstaendigt bekjendt Gruppe af Krebsdyr Pachybdella o.s.v., 

 Oversigt o. d. K. D. Vid. Selsk. Forhandl Kjipbenhavn, pp. 127-131, 1855. 



