REPORT ON THE NEMERTEA. 37 



the different paragraphs, which are more especially devoted to the internal anatomy of the 

 different representatives of the sjaecies, that are here described in their systematic 

 arrangement. 



C. SCHIZONEMERTEA. 



Family L i n E i d .^. 



Cerebratulus, Ren. 



To this genus I wish to refer all the Schizonemertea collected by the Challenger. I 

 have elsewhere (VIIl) insisted on the difficulty of distinguishing the genera Cerebratulus, 

 Lineus, Micrura, &c., of which perhaps the two first may be distinguished by an 

 ontogenic difference {Pilidium or Desor-larva). And even this distinction is not 

 definitely established. It is simply impossible to refer spirit specimens to any one of 

 these genera rather than to any other, and having formerly included Micrura as a 

 sjTionym amongst Cerebratulus, I now even feel inclined to do the same with Lineus. 

 What value has a generic distinction when it can never be of any use to a taxonomist ? 

 And why should a developmental difference, such as that which obtains l)etween a 

 Pilidium and a Desor larva, not be sufficiently honoured by a sjiecific distinction ? 



As to describing new species in this genus, it is even more difficult than in any other, 

 because of the number already existing, which are partly solely distinguished by their 

 coloration in life, a character not available in determining the Challenger specimens. 

 Hence, only in seven cases can I hold myself justified in referring the fragments to separate 

 species, six of which are new. The remaining fragments and heads, which clearly show 

 the Cerebratulus type (e.g., PI. XV. fig. 8), I will not specifically distinguish; what 

 remarks I have to make about them wdl appear when treating of the anatomy, and 

 will then be noticed as pertaining to the genus Cerchratidus in general. 



Following the order of succession of the stations at which the Schizonemertea were 

 successively dredged during the expedition, we will now proceed to describe them. 



Cerebratidus truncatus, n. sp. (PL I. figs. 11, 12). 



This species, collected on the coast of Nova Scotia, and, as we refer a specimen from 

 Bermuda to it, also frequenting the ocean in the vicinity of those islands, was captured 

 May 8, 1873 (Le Have Bank), and once more, on May 20 of that year, when it came 

 from a depth of 85 fathoms at Station 49. 



The anterior part of these two specimens is figured on PL 1. figs. 11, 12, the first 

 Ijeing a side view, the second a ventral \dew, the latter more considerably, the former 

 about four times enlarged. From both figures it is seen that the mouth is small and close 



