4i 



I have nothing to mention about Chaetoderma nitidulum. I will here write down my obser- 

 vations of the radula of the other forms, a fuller description of which I hope soon to publish ; 

 for comparison is facilitated when all the figures with relation to the radula of Chaetoderma 

 are within our reach. 



Figs. 214 and 215 represent sections of a species of Chaetoderma of unknown origin. There 

 beino- many points of conformity I feel justified in classing this specimen among Chaetoderma 

 Lovéni. The radula corresponds with that of Chaetoderma Lovéni; the large tooth dt, broken 

 here, the side-pieces d, the sickle-shaped teeth a and more especially the narrow oblong piece 

 ó, broken here also. 



Figs. 2 1 2 and 2 1 3 represent the radula of a species of Chaetoderma of unknown origin 

 (present of Rev. Norman) which for the rest does not differ much from Chaetoderma nitidulum. 

 The large tooth dt and the side-pieces d are present; it is distinctly visible that the small 

 chitinous radula consists of a heart-shaped centre, 2 large and 2 smaller curved teeth and some 

 small ones. 



Fig. 2 1 1 represents the radula of a species of Chaetoderma from Port-Hood (Canada) 

 which I intend to call Chaetoderma canadense. After isolation with Eau de Javelle the large 

 radular tooth is found whilst the 2 very small teeth noticed for Chaetoderma nitidulum are also 

 present; the latter are oblong, somewhat spindle-shaped, slightly curved but not sickle-shaped. 

 In the isolating the small teeth have changed places, but probably their positions were 

 similar to those of the teeth of Chaetoderma nitidulum (cf. Kowalevsky 13, fig. 27). To render 

 a comparison between the two radulas possible, I also give that of Chaetoderma nitidulum, 

 after isolation with Eau de Javelle (fig. 216); here the little teeth have also changed places : 

 in "canadense" there is however more difference in size between the large tooth and the small 

 ones, than there is in "nitidulum". 



For Chaetoderma we can therefore distinguish 3 types of a radula : 

 i° 1 large tooth upon which 2 smaller teeth are placed : Chaetoderma nitidulum, productum 



and canadense. 

 2 1 large tooth upon which there is a row of teeth : Chaetoderma gutturosum, Lovéni, Wiréni 



and the above mentioned species of Norman (and "militare"?). 

 3 Several rows of 5 teeth, one behind the other. No large tooth : Chaetoderma radulifera. 



Now we will look, whether there is any relation between these 3 groups. In "radulifera" 

 there are rows which consist of 5 teeth, but what do we observe in group 2 ? For this let 

 us compare Kowalevsky's figures 24 and 26 with my figures 191 — 194. The large tooth dt 

 is present in both forms ; my side-teeth d may be compared with d and d' of "gutturosum"; 

 in "Lovéni" there are however only 2 such pieces. On comparing the sickle-shaped pieces a 

 we notice an important difference; whilst in "gutturosum" the pieces a form a closed ring, 

 they are in "Lovéni" visibly provided each with a small chitinous tooth; in the sections these 

 yellow teeth are clearly distinct from the evidently cuticular sickles. Kowalevsky does not 

 mention anything about this, neither does he say whether the sickle-shaped pieces of "gutturosum" 

 consist of chitine or not. Upon d a chitinous tooth is likewise met with; "gutturosum" is however 

 without the rectangular piece b. We may speak here too of a row of 5 teeth ; 2 chitinous 



SIBOGA-EXPEDITIE XI. VII. 



