DESCRIPTIONS OF GENERA AND SPECIES 685 



The setae, except for the apparent absence of ornamentation, which, I imagine, 

 requires confirmation, are, judging from the figures in the papers above quoted, 

 exactly like those of 8. millsoni. 



(a) Siphonogaster millsoni, BEDDAKD. 

 S. millsoni, BEDDA.RD, P. Z. S., 1891, p. 48. 



Definition. Dimensions about the same as in the last species. Body markedly quadrangular 



posteriorly. Setae ornamented. Penial setae arranged more or less regularly in two rows. 

 Hob. Lagos. 



The above points are all the differences which the published descriptions of the 

 species allow me to extract. S. millsoni has been described more fully than the 

 others, and by myself (39). The setae are most distinctly ornamented, the ordinary 

 setae as well as the penial. For the habits of this, the ' Yoruba-worm,' see MILLSON. 



The quadrangular form of the body appears to be very characteristic of the 

 species. In transverse sections (of which no description was given in my paper 

 upon the worm) the body-wall is seen to be greatly thickened at the four corners ; 

 the thickening is entirely at the expense of the longitudinal muscular layers ; the 

 dorsal, ventral, and lateral surfaces are comparatively thin, particularly the dorsal. 

 The outline of such sections forms an oblong, the lateral diameter being greater 

 than the dorso -ventral. 



The nephridia are paired structures, and their external pores are related to the 

 ventral setae. There is not a terminal muscular sac present. They do not begin 

 before the fifteenth segment. The vascular system is remarkable for the fact that 

 there are two subnervian vessels running in close contact with the body-wall, along 

 the two sides of the nerve-cord ; they are each about one-half of the size of the 

 ventral blood-vessel. There seems to be no supra-oesophageal blood-vessel ; in 

 segments viii-xii are hearts connecting the dorsal and ventral blood-vessels. 



The oesophagus (without a gizzard) extends back to segment xvii ; after segment ix 

 its walls are very vascular ; the intestine is sharply marked off from the oesophagus 

 by its much taller epithelium, and by the much feebler vascular supply. The intestine 

 is for. the space of one segment no wider than the oesophagus which precedes it; this 

 region too has a taller epithelium ; in the eighteenth segment it suddenly widens out, 

 but does not begin to show the regular and characteristic constriction for three 

 segments after this. The muscular coat of these two parts of the intestine is very 

 much thickened, and, although the lining epithelium, as already mentioned, is ciliated 



