210 Annals of the South African Museum. 



feature of this region is the great development of the genital pleurae. 

 In the undisturbed living animal their free edges overlapped each 

 other to a considerable extent, especially in the region behind the 

 gills ; they adhered rather firmly at their edges, and formed a long 

 tubular structure. At their point of attachment to the collar their 

 edges were closely appressed, but did not overlap. 



Just behind the collar the body was slightly greater in diameter 

 than the collar, both in the living (11 mm.) and in the preserved 

 state (10 mm.) This became somewhat less posteriorly in the folded 

 condition. When spread out, the genital pleurae at the gill region 

 measured about 11 mm. from the edge of the one to the edge of the 

 other ; behind the gill region it was about 15 mm. throughout, this 

 being about the breadth of the remaining three pieces of this region. 

 The pleurae end abruptly. 



The glandular stripes of epithelium on the outside of this region 

 and the colour here are worthy of notice. The former were very dis- 

 tinct, being half a millimetre in breadth anteriorly and often forming 

 continuous bands from the mid-ventral line to the edges of the genital 

 pleurae. In a distinct furrow lay the nerve chord, appearing as a 

 slightly elevated ridge about -3 mm. in diameter, and with transverse 

 stripes corresponding to the glandular ridges on each side. 



The same general disposition of parts was seen on the second 

 fragment, but towards the middle a differentiation began to appear, 

 viz., the transverse lines became more irregular and discontinuous 

 towards the margin of the pleurae, while retaining their regularity in 

 the immediate neighbourhood of the ventral nerve chord. Towards 

 the posterior these regions became partly marked off from each other 

 by a longitudinal furrow on each side, commencing first on the right 

 side. In the third and fourth fragment this was more marked, and 

 took the form of two rather deep furrows, one on each side, at a 

 distance of about 2 mm. from the mid-ventral line, so as to give an 

 appearance of a second but very small pair of pleurae (cf. Schizo- 

 cardium). The epithelium of these folds had very regular transverse 

 stripes of glandular patches, which sometimes were continued over 

 the nerve chord (which appeared here as a ridge with no groove) to 

 those on the other side, sometimes ended abruptly at the nerve, 

 alternating in position with them. The area between the folds thus 

 formed a longitudinal band about 4 mm. in breadth, distinctly 

 marked off from the area on each side (each about 6 mm. in breadth). 

 This ventral band appeared on the third and smallest fragment, 

 which also included pai't of the hepatic region, but was not continued 

 further backwards. 



