' ANATOMY AND CLASSIFICATION OF THE ARENICOLlD^. 429 



most only one posterior abranchiate segment^ which, as men- 

 tioned above (p. 426), is frequently found in specimens of 

 A. Grubii. The only differences between these forms are 

 connected with the colour and number of gills. 



The colour of A. Grubii varies within wide limits, for in 

 one gathering at Port St. Mary we have taken specimens of 

 this species varying in colour from dark green through dark 

 red to reddish yellow. The number of gills described as 

 occurring in A. cyanea, A. dioscurica, and A. Bobretz- 

 kii is respectively thirteen, fifteen, and twenty pairs. This 

 difference is probably explained by the different ages of the 

 specimens chosen as typical of the species. 



A. Boeckii, Rathke, as described by him (1843, p. 181, 

 and pi. viii, figs. 19 — 22), is an indubitable but probably 

 young A. ecaudata, as it has the first gill on the sixteenth 

 chsetigerous segment, and has forty pairs of gills. Speci- 

 mens agreeing with Rathke's description have been sub- 

 mitted to us, and after a careful examination of their external 

 characters, and of some points in their internal anatomy, we 

 consider them to be young forms of A. ecaudata (see p. 423). 

 Clymenides ecaudatus, Mesnil (1897), is the post-larval 

 form of A. ecaudata. 



A. pusilla, de Quatrefages,^ of which only a single in- 

 complete specimen is known, from Coquimbo : A. assimilis, 

 Ehlers,^ from the Straits of Magellan : and A. Loreni, 

 Kinberg,^ from the Cape : are so shortly and insufficiently 

 described, that for all practical purposes they must be 

 ignored. 



Habits. 



(1) Arenicola Grubii and A. ecaudata. 



On the coast of the Isle of Man, at Port Erin and Port 

 St. Mary, and at Plymouth, A. Grubii and A. ecaudata 



1 'Hist, des Anueles,' tome 2, part i, p. 266, 1865, Paris. 



2 'Magalliaen. Sanmiel Reise-Polycbseteu,' Hamburg, p. 103, 1897. 



' ' Kong. Sveiiska Fregatt. Eugenies Resa,' 1857, and * Aunulata nova 

 Recensuit," ' Oefv. k. Vet. Akad. ForLandl.,' 1865, p. 355. 



