41 



I have nothino- 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 ho|>e soon to publish ; 

 for comparison is facilitate'd when all the fit,rures with relation to the radula of Chaetoderma 

 are within our reach. 



I'io-s. 214 and 215 rejiresent sections of a species of Chaetoderma of unknown origin. There 

 beintr manv points of conformity I feel justified in classing this specimen among Chaetoderma 

 Loveni. The radula corresponds with that of Chaetoderma Loveni; the large tooth <//, broken 

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

 d, broken here also. 



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

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

 The large tooth df 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. 211 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. Kowalevskv 13, fig. 27). To render 

 a comparison between the two radulas possible, 1 also give that of Chaetoderma nitidulum, 

 after isolation with Fau de Javelle (fig. 216); here the litde 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 : 

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



and canadense. 

 2" I large tooth upon which there is a row of teeth : Chaetoderma gutturosum, Loveni, \\ ireni 



and the above mentioned species of Norm.\n (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 tlo we observe in group 2 r I'or this let 

 us compare Kowalevskv's figures 24 and 26 with m\- figures 191 — 194. The large tooth (// 

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

 in "Loveni" 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 "Loveni" visibly provided each with a small chitinous tooth; in the sections these 

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

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

 consist of chitine or not. I'pon da. chitinous tooth is likewise met with; "gutturosum" is however 

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



SIBOGA-EXPEDITIE Xl.Vlt. 6 



