DESCRIPTIONS OF GENERA AND SPECIES 659 



British Guiana, I found the setae to be paired throughout the body; FRITZ MULLER 

 has noted the occasional occurrence of species with wholly paired setae. 



The clitellurn is another structure which varies in extent, as indicated in the 

 description of the species ; in one individual (from British Guiana) I observed a 

 clitellum of only four segments (xviii-xxi). The clitellum is saddle-shaped, but the 

 width of the ventral bare tract is apt to vary in different parts of the clitellum ; 

 on segments xvi-xviii of the clitellum in two individuals from British Guiana the 

 bare space was extremely narrow widening gradually on the last ; on segments 

 xix-xxiii it was the double of its former width. The clitellum is orange coloured 

 in the living worm, the rest of the body reddish, owing to absence of pigment. 



The nephridiopores commence on the fourth segment ; those of the ' mucous 

 glands ' open on ii. It has generally been stated that this species has no prostomium. 

 MULLEE, on the contrary, asserted the existence of one, and HORST has figured 

 (17, PI. iii, fig. 33) and described something very like a prostomium ; the worm has 

 the habit of inverting the first segment which conceals the prostomium. 



(2) Pontoscolex arenicola, SCHMARDA. 

 P. arenicola, SoHMARDA, Neue wirbell. Thiere, I. ii, 1861, p. 11 (in part.). 



Definition. Anterior setae as well as those upon the clitellum ornamented ; two pairs of 

 spermathecae dilated at extremity into a reniform pouch. Hob. Jamaica ; sea-shore. 



Under the name of P. arenicola, SCHMARDA confounded no less than 'three 

 distinct species of earthworms, all of which were found upon the sea-shore on the 

 island of Jamaica ; one of these is the present species, the other is a Diackaeta 

 D. littoralis (see p. 663), the third a Pontodrilus, which I cannot distinguish from 

 P. bermudensis. P. arenicola does not show many points of difference from 

 P. corethrura ,- the principal differences are mentioned in the diagnosis ; the 

 setae have the same irregular arrangement posteriorly; anteriorly they are paired; 

 and at the hinder end of the body they have a regular quincuncial disposition ; in 

 P. corethrura the setae upon the clitellum are ornamented, the other setae having 

 mere traces of the transverse ridges which are found upon the clitellar setae. In 

 the present species the setae in front of the clitellum are also ornamented in the 

 same way as are the clitellar setae, only differing from them in their greater size ; 

 I did not detect a bifid extremity; but this is often hard to detect in P. coretkrura. 



SCHMARDA has mentioned that the alimentary canal is furnished with '4 braune 

 birnformige Organe ' ; these I take to be the calciferous glands, which are, however, 



4 r 2 



