408 THE OFISTHOBRANOHIATE 



increase indicates growth through stages possessing central teeth of 

 smaller, not of larger, size. 



At the same time I cannot place the same confidence in inferences 

 drawn from measurements of the teeth in Nos. 12, 13, and 14, for 

 these teeth are shrunken and distorted, owing to the method in which 

 the radulse were mounted. No. 8 was also mounted dry, and it 

 may be noticed that the teeth in this specimen show a considerable 

 reduction in width compared with Nos. 7 and 9. As it has been 

 shown above that in many points of structure increased age brings 

 about a closer and closer resemblance of the teeth of A. ^punctata to 

 those of large examples of A. depilans, I am inclined to give more 

 weight to this trustworthy evidence than to that afforded by the 

 shrunken teeth of Nos. 12, 13, and 14 ; and in the absence of any 

 definite statements upon the matter by Mediterranean zoologists I 

 think considerable grounds are afforded by this examination of the 

 teeth for regarding A. depilans as merely A. punctata modified by 

 further growth. I trust that the subject may receive more conclu- 

 sive treatment in the hands of a naturalist upon a coast where large 

 Aplysise are more common than they are with us in England. It 

 is especially needful that the young A. depilans should be identified 

 and described. 



While upon the subject of the teeth of Aplysia I may add that 

 Dr. J. E. Gray, in his Guide to the Distribution of the Mollusca in 

 the British Museum, 1857 (p. 200), gives a description of the teeth of 

 A. depilans and A. punctata which is very difficult to understand. 

 For A. depilans he describes a radula having a formula 12"1'12, 

 of which the central tooth is " distinct and truncated, triangular, 

 dilated beneath.,^ with an arched front edge ; apex truncated, re- 

 flexed ; reflexed part subcordate, dark, with three large toothlets in 

 front." Is this a true depilans at an early stage ? For A. punctata 

 he says, " Central tooth with the base on each side expanded ; apex 

 recurved, with one sharp point lobed on both sides ; lateral teeth about 

 thir een.'^ 



Curiously enough, this latter description is veiy applicable to the 

 figure given by Mr. Jabez Hogg^ of the central tooth of an A. 

 hybrida from Torbay, which numbered " seventy-two rows of diver- 

 gent teeth,'' but possessed " numerous laterals." Certainly I have 

 seen no A. punctata having this number of rows of teeth or this 

 structure, although Mr. Hogg's figure closely corresponds with that 

 given by Vayssiere for A. punctata. I wish to thank Mr. Hogg 

 for his kindness in lending me a copy of his original paper at a 

 time when it was impossible to obtain one from the libraries. Fig. 



1 The italics are mine. 



2 The Lingual Membrane of Mollusca, Trans. Micr. Soc, xvi, N. S., pi. x, fig. 42. 



