A7'e7iicola c vis tat a 109 



than those mentioned ahove ; they usually range in length from 

 about 200 mm. to 300 mm. (tail ahout GO to 100 mm.). 



The Neapolitan are more slender than the American specimens, 

 especially in the tail region (c/. Figs. 12, 13, PI. V). The former are 

 stated by Lo Bianco (1893) to attain a length of 400 una. ; ten 

 specimens seen by the writer were from 200 to 300 mm. long. The 

 examples from Suez were smaller, namely, 120 to 185 mm. in length. 



Colour. — In life A. cristata displays beautiful colouration. In 

 Neapolitan specimens the greater part of the body generally exhibits 

 a fine dark green colour, with play of iridescence ; sometimes the 

 middle region is brown. The gills are almost invariably of a ricli 

 dark red or deep crimson colour, and the notopodial chaetae golden 

 yellow. American and "West Indian examples seem to exhibit similar 

 colouration, according to the accounts of Stimpson, Verrill and otliers. 

 Mr. Crossland found, among the examples collected at Suez, two of a 

 deep greenish-black colour, and others were yellowish or pinkish. 



Variations ix the Organs. — The first gill is subject to consider- 

 able variation in size, but it is rarely wanting. In one specimen a 

 very small additional gill is present, namely, on the left side of the 

 sixth segment; this is the only specimen of Arcnicola, out of some 

 thousands seen l)y the writer, in which a gill occurs in front of tlie 

 seventh segment. 



In American examples of this species the tail usually consists of 

 few segments, about seven to ten ; ^ each specimen, when adult, has 

 therefore about thirty caudal segments fewer than it had in the post- 

 larval stage, due to loss of segments from the posterior end. Each 

 tail-segment consists of a large aunulus and a number of smaller 

 ones ; the former Ijears a series of hollow thumb-shaped processes, 

 which are generally largest in the first caudal segment, where they 

 attain a length of about 2 mm. Occasionally the most dorsal one is 

 branched distally and resembles a small gill (1*1. Y, Fig. 13). The 

 morphology of these processes is obscure ; it has been suggested that 

 they are rudimentary gills, and the position and branching of the 

 dorsal member of the series lends some support to this view, but 

 there is no evidence that the more ventrally placed outgrowths are 

 more than exaggerated epidermal papillae. There is some variation 

 in the degi-ee of development of the processes, even in specimens 

 from neighbouring localities ; but, as a rule, they are well developed 



' One specimen has seventeen tail segments. 



