is also possible that the spicula are hollow and merely consist of cuticular matter. A cubical 

 epithelial layer surrounds them. Somewhat proximally from the cloaca-opening they appear on 

 the outside; here next to the left spiculum a smaller one is observed (fig. 165). 



The heart does not furnish any peculiarities. Fig. 162 represents 2 proximal offsets 

 of the pericardium, the median walls of which are invaginated. Both invaginations unite and 

 form the atrium (fig. IÖ3«), continuous with the ventricle, an invagination of the dorsal pericardial 

 wall more proximally (figs. 164, 165 e 1 ). A dorsal and ventral blood-sinus are present. Around 

 the gills a great number of blood-corpuscles are found, but no distinct blood-sinuses. The blood 

 consists of a very finely granular liquid, staining pale red, in which the blood-corpuscles are found. 



It is impossible to follow the course of the nerves in the anterior part of the body amid 

 the numerous muscular fibres and glandular cells. The ganglion posterius superius is distinct 

 (fig. 162), as well as the commissure between the ganglia posteriora inferiora; but the commis- 

 sures between the ganglion posterius superius and the ganglia posteriora inferiora are absent. 



The thick cuticle and the spicula remind us of Proneomenia, but the absence of 

 papillae, the distichous radula, the structure of the salivary glands and the presence of gills 

 are important points of difference. We see at once that it is related to Proparamenia and 

 Paramenia, but from the former it directly differs on account of the distichous radula. The 

 following are the points of resemblance it presents to Paramenia : the distichous radula, the 

 gills, the absence of papillae in the integument, the presence of some papillae on the ventral 

 side (cf. Pruvot 4 fig. 61), and, though in a lesser degree, the structure of the cloaca-ducts. 

 It is however advisable to keep both forms separate. In structure as well as in size the radula 

 and radula-sac diverge from those of Paramenia. The salivary glands are also of a different 

 structure and situation. In Paramenia the nervous system in the distal body-part is different 

 and the cuticle much thinner. It cannot be denied however that there is a close relation 

 between both forms. 



Dondersia. 



11. Dondersia annulata nov. spec. (Plate V, figs. 172 — 179). 



Stat. 47. Bay of Bima (N. Sumbawa). 55 M. Upon Gorgonid. 1 Specimen. 



Length-index 48. Pale brown with 30 white non-closed rings. 3 dorso-terminal sense- 

 knots. 1 pair of vesicular appendages of the cloaca-ducts. 

 East-Indian Archipelago. 1 Specimen. 



Fig. 172 represents the animal, 4 times enlarged. The length is 29 mm.; average 

 diameter 0.6 mm.; the length-index is therefore 48. The animal has contracted very irregularly, 

 the transverse sections being consequently of very different sizes. The colour is a pale yellowish- 

 brown with a greyish gloss, owing to the spicula. 30 white rings occur, placed at irregular 

 distances from each other, not closed, but open on the ventral side. The ventral groove is visible 

 as a very narrow slit. The posterior part has a projecting lip (/>), opening into the alimentary 

 canal on the ventral side (;;/). 



SIBOGA-EXPEDITIE XLVII. 5 



