Arenicola pusilla 121 



belonging probably to tlie species A. pnsilla. The description and 

 figures are, however, in agreement with A. hranchialis 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, oven then, recognise the difference 

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

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

 A. piscatorum. It is proliable tliat the earlier record also referred in 

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

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



Bionomics. — A. pusilla is nuxlerately common in sliaUow water, 

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

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

 e.g. near the outfall of drains. Lo Bianco states that iu 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 Xaples for some weeks, are similar to 

 those of A. marina. 



Examples taken by Brof. A. D. Howard in Buget Sound were 

 found generally in ortlinary sandy beaclies, but two larger specimens 

 were burrowing in a coarse gravelly and rocky beach. 



Size. — Neapolitan specimens are usually small — not more tlian 

 60 to 70 mm. in length. Lu Bianco states tliat 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 Bacific attain a greater size — 130-175 mm. in 

 length.^ 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 nnn., but its tail is of extraordinary length 

 (117 mm.), probably due to extreme relaxation ^os^7nor<cw. 



