40 



Chaetoderma Lovéni; on looking at fig. 208, which represents a part of it, 125 times enlarged; 

 the entire difference trom fig. 185 (215 1 is directly noticed. 



Here also the longitudinal muscular bundies do not form 4 muscular regions but 1 

 thin continuous layer. The retractors m, tri and tri' (figs. 206, 207) are also present here, but 

 they are much more strongly developed than they are in the preceding species. 



The structure of the organs of the proximal part corresponds in some degree with that 

 of Chaetoderma Lovéni. The pharynx bas strongly contracted, in consequence of which the 

 mouth-opening is retracted and lies in a cavity (cf. figs. 188 and 206). The salivary glands are 

 present but I cannot demonstrate any buccal glands. I must make mention of the fact that 

 here too the intestine carries a small proximal coecum. 



The structure of the nervous system coincides with that of Chaetoderma Lovéni; the 

 sublingual commissure is clearly discernible and provided with some small nerve-knots (cf. Wirén, 

 6 a pi. VII, fig. 1). 



The radula is noteworthy (figs. 209 — 210). The large tooth dt is present, as well as 

 the side-pieces d, which here are visibly provided with a chitinous covering. The 2 sickle- 

 shaped pieces a are also easily discernible and consist merely of chïtine. The other pieces are 

 fragments, the original situation of which cannot be traced. The narrow oblong piece b present 

 in Chaetoderma Lovéni is wanting in Chaetoderma Wiréni, which has only curved teeth ; 

 therefore there is a difference between the two forms in the structure of the radula. 



The liver is large and of a similar structure to that of Chaetoderma nitidulum. The 

 genital gland is mature and compactly filled with spermatozoa. Of the organs of the posterior 

 body-part hardly anything has been preserved. 



The number of the gill-lamellae can be indicated with certainty and is about 20. 



Chaetoderma Wiréni differs in the first place from the known species of Chaetoderma on 

 account of the spicula, the shape of which may be compared with that of Chaetoderma niti- 

 dulum, gutturosum and radulifera. Vet it has to be kept distinct from these three forms on 

 account of the structure of the radula. 



III. ON THE RADULA OF CHAETODERMA. 



(Plate VI, figs. 211 — 216). 



Especially after what has recently been published by Kowalevsky (13) it may be desirable 

 to give a short account of what is known of the radula of Chaetoderma. The fact, that the 

 radula of Chaetoderma is composed of different teeth is not new, when we remember what 

 Hubrecht (3 pag. 5 note) has written about it. Three years ago already I examined different 

 species of Chaetoderma and as I always met with a radula, consisting of different teeth I tried 

 to indicate one for Chaetoderma nitidulum too. I isolated the radula of this form with Eau de 

 Javelle, and like Kowalevsky I found the 2 small teeth situated upon the large one. Though 



