Arenicola pusilla 121 



belonging probably to the species A. pusilla. The description and 

 figures are, however, in agreement with A. branchialis in several 

 striking points, namely, the absence of tail and of dilatation of the 

 anterior region of the body, the repeated dichotomous branching of 

 the gills, the single pair of oesophageal glands and the size and 

 shape of the septal pouches. It is clear from Delle Chiaje's later 

 memoir (1841) that he did not, even then, recognise the difference 

 between a caudate and an ecaudate Arenicola, for he referred speci- 

 mens, some of which were undoubtedly A. branchialis, to the species 

 A. piscatorum. It is probable that the earlier record also referred in 

 part to A. branchialis. The carelessly drawn figure in Delle Chiaje's 

 memoir formed the basis for the genus Chorizobranchus (see p. 32). 



BIONOMICS. A. pusilla is moderately common in shallow water, 

 down to about six metres, in parts of the Bay of Naples, where the 

 bottom is muddy ; it is abundant where organic matter is plentiful, 

 e.g. near the outfall of drains. Lo Bianco states that in summer the 

 worm either disappears or is found only rarely. 



The general habits of this species, which the writer had an 

 opportunity of observing in Naples for some weeks, are similar to 

 those of A. marina. 



Examples taken by Prof. A. D. Howard in Puget Sound were 

 found generally in ordinary sandy beaches, but twq larger specimens 

 were burrowing in a coarse gravelly and rocky beach. 



SIZE. Neapolitan specimens are usually small not more than 

 60 to 70 mm. in length. Lo Bianco states that they may attain a 

 length of 150 mm., but that is an exceptional size; the writer has 

 not seen, among the numerous Neapolitan specimens he has examined, 

 any exceeding 100 mm. in length. 



Examples from the Pacific attain a greater size 130-175 mm. in 

 length. 1 Those from Dutch Harbour, Unalaska, are the largest known 

 examples of the species; their length, 160 mm., is not remarkable, 

 but they are of very massive build, being. 50 to 60 mm. in girth at 

 the widest point. 



COLOUK, Small Neapolitan specimens are pink and semi-trans- 

 parent, so that the blood-vessels and internal organs can be well 

 seen. In most cases there is a darkening, a " smoky " appearance, 



1 One reaches the length of 207 mm., but its tail is of extraordinary length 

 (117 mm.), probably due to extreme relaxation post-mortem. 



