ANATOMY AND CLASSIFICATION OF THE ARENICOLTD^. 547 



septa of this family, so far as is known,^ are, however, widely 

 different from those of Are iii col a. In fact, until knowledge 

 of Chlorhsemid anatomy and development is in a more 

 advanced condition, any conclusion as to the affinities of this 

 family must appear premature. 



17. Summary of Results. 



I. In this paper we show that there are three British 

 species of Arenicola — A. marina, A. ecaudata, and A. 

 Grubii. The last has not hitherto been recognised as a 

 member of the British fauna. It has, no doubt, often been 

 mistaken for A. ecaudata. From the Pacific coast of 

 America we record A. Claparedii, hitherto only known from 

 the Mediterranean. 



II. The anatomy of A. Claparedii and A. cristata is 

 fully described for the first time. 



III. The genus Arenicola may be divided into two 

 sections, according to the characters of the prostomium, the 

 arrangement of the gills and setae, the form of the ventral 

 lip of the nephrostome, and other features. To the first 

 section belong the common lugworm (A. marina), A. Cla- 

 paredii, and A. cristata, in which the prostomium is 

 well developed, the gills and setse are not continued to the 

 end of the body (i. e. there is an achtetous and abranchiate 

 "td,\\"), and the ventral lip of the nephrostome is entire. 

 The second section includes A. ecaudata and A. Grubii, in 

 which the prostomium is reduced, the gills and sette are 

 continued to the posterior end of the body, and the ventral 

 lip of the nephrostome is deeply notched at its centre. 



IV. The external features usually relied upon by chseto- 

 podists to distinguish these five species from each other are 

 liable to such great variation in different specimens and in 

 the life history of the individual as to render them (taken 

 alone) insufficient for accurate diagnosis. The characters of 

 the otocysts, prostomium, and nephridia taken together 

 afford a far more reliable basis for specific determination. 



1 See Bles (1892). 

 VOL. 43, PART 3. — NEW SERIES. p P 



