26 BRITISH COPEPODA. 



Series 2. P(ECTL0ST0ma. 

 Os mandibulis et siphone carens, maxillarum paribus 

 3 — -1 ( — 0) instructum. 



Series 3. Siphonostoma. 



Os in siplionem, mandibulas 2 plerumque inclu- 

 dentem, productum, et maxillarum paribus 3 — in- 

 structum. 



As regards tlie debateable anatomical points, it may 

 be useful if I quote, in the first place, some remarks 

 of M. Thorell, taken from a letter wliicb he was good 

 enough to address to me some few years ago — before 

 the publication of Dr. Claus's 'Neue Beitrage zur 

 Kenntniss parasitischer Copepoden.' M. Thorell writes 

 as follows : — " You know, of course, that I have pro- 

 posed to divide the Oopepoda into three parallel series, 

 Grnathostoma, Poecilostoma, and Siphonostoma, and 

 that I consider the Poecilostoma to be characterized 

 by having the parts of the mouth free, and formed 

 for stinging or liching, as also by the mandible being 

 absent. This view of the oral apparatus of the Psecil- 

 ostoma has been accepted by Claparede and a few 

 others, but it is not admitted by, for instance, Glaus, 

 who considers that the Poecilostoma have true man- 

 dibles, and who rejects the subdivision proposed by me. 

 The reasons which induced me to believe that the 

 Psecilostoma were destitute of mandibles, and that 

 what Glaus calls mandibles are the true maxillse, and 

 that his maxillse are maxillar-palpi, were — first, that 

 the "mandibles" are always placed far more back- 

 wards than the true mandibles of the Guathostoma : 



