[ 371 ] 

 VII. On British Annelida. By W. C. M'Intosh, C.M.Z.S. 



Read May 19th, 1874. 



[Plates LXVII.-LXX.] 



Paet I. — EuPHROSYNiD^, Amphixomid.e, Aphrobitid^, Poltnoid^, Acoetid^, 



and SiGALioNiD^. 



In the first of a series of papers on the British Marine Annelida, which I propose to 

 offer to the Society, one or two reflections which have occurred during the study of the 

 present forms may not be inappropriate, especially as they apply with equal force to the 

 succeeding groups. Few students of the'Aunelida proceed far in their investigations 

 before becoming aware that in many of the descriptions of their predecessors there is 

 nothing decisive, and that they must wade through many superficial remarks without 

 being able to lay hold of any stable character by which to extricate themselves from 

 doubt. In some cases it would almost seem that the authors meant their successors to 

 spend valuable time to little purpose in vainly endeavouring to find out the exact 

 nature of the species, of which they themselves entertained only a hazy conception. 

 It would appear in the majority of these instances that such inadequate and unsatis- 

 factory descriptions have been due to the fact that the nice distinctions between closely 

 allied forms have hitherto attracted little attention and less study. It is impossible, 

 for example, to describe too minutely in groups like the Polynoidee, in which the 

 specific separation rests on so many fine characters. The mere statement that a 

 bristle is slender and serrated conveys little more to the mind of an observer than the 

 assertion, in comparing the hair of the bat with that of the sheep, that each is 

 serrated. Even some of the most distinguished modern investigators of the Annelida 

 have failed to appreciate the valuable results derived from a strict and faithful appre- 

 hension of the structure of the bristles, the other characters of course being duly 

 attended to. If, instead of writing pages of weary Latin descriptions, a few terse 

 sentences had been given, and a single characteristic bristle accurately figured by 

 the author, very great labour and not a little doubt would have been saved to his 

 successors. The characteristic markings at the tips of the bristles of Hermadion pellu- 

 cidujn and H. assimile, for instance, show how valuable such characters will some day 

 be in classification. The same peculiar feature is exhibited by the Gastrolepidia clavi- 

 gera of Schmarda in the upper series of the ventral branch of the foot, and in the 

 whole of the dorsal bristles ; moreover their transparency is remarkable. The di- 

 stinctions between many of the species are nice, yet exact, and aflford a good field for 

 VOL. IX. — PAKT VII. January, 1876. 3 e 



