19(5 ASPIDOSIPHON CYLINDBICUS. 



of the trunk the body-wall is rather thick, marked by 

 annular grooves ; in its posterior half, however, the skin is 

 plain and thin , and the retractor-muscles and nephridia 

 are visible through it. On a distance of 3 mm. from the 

 terminal shield, nearly on the place where the retractor- 

 muscles are attached to the body-wall, the skin shows a 

 girdle-shaped area of a glistering appearance. The cutaneous 

 bodies (Hautkörper) are not very densely scattered over 

 the surface of the body; they resemble those of ^. Steenstrupii 

 (Selenka, die Sipunculiden, taf. XIII, fig. 191), but only 

 a single glandular opening could be detected , somewhat 

 by the side of the centre. The anterior and posterior shields 

 have about the same size , but not the same shape ; the 

 first of them is elliptical and lies at an oblique angle to 

 the trunk. It is convex and divided in a great number of 

 small polygonal areas, consisting of a dark brown chitinous 

 substance ; on the passage between this shield and the 

 adjacent skin , similar areas are visible over a narrow 

 space, but they are only surrounded by a dark brown 

 margin. The posterior or terminal shield is of a paler 

 colour, circular and concave; its margin is also divided by 

 grooves in numerous polygonal areas. 



The proboscis or introvert is very short, about 8 mm. 

 long, though he may perhaps not be totally protruded. 

 Its terminal part is, over a third of its length, densely 

 beset with parallel rows of small brown hooks, the remain- 

 ing posterior part showing larger hooks, irregularly 

 scattered. The smaller hooks (fig. 4) are only 0.048 mm. 

 high ; they have the shape of a triangular pyramid , with 

 a large convex face and two smaller concave ones. 

 The edge between the two latter faces bears a small , 

 hardly visible tooth in its basal half. The hooks of the 

 basal part of the proboscis are two and a half times larger 

 and look like conical spines, faintly bent and furnished 

 near their base with several prominent ridges. Between 

 both kinds of hooks the usual conical excretory ducts of 

 glands can be observed. 



Notes from the Leyden IMuseiiiii, Vol. XX. 



