318 THE DOLABELLINAE. 



been broken off accidentally. In all the other rows of the radula this mal- 

 formed tooth appears in a corresponding position to those here figured. 



Our information respecting the dentition of the Dolabellinae is very meagre, 

 being limited to a paper by Mazzarelli and Zuccardi (1890), one by Eliot (1899), 

 one by Farran (1905), two by Bergh (1905, 1907), one by Vayssiere (1906) and 

 the figures given by Pilsbry in Tryon's Manual, 16, Plate 67, fig. 17, 18. In these 

 papers the radulas of five species are described of the fifteen or twenty more or 

 less doubtful species which have been recorded. In general a uniform type of 

 dentition prevails, the number of rows and the number of teeth in each row 

 being indefinite, and varying with the size and age of the animal. The dental 

 formula of D. scapula, for example, ranges from 44 X 120-1-120 (Farran) to 

 45-60 X 120-160-1-120-160 (Vayssiere), and 60 X 200-1-200 (Bergh). The 

 formula for D. agassizi is at present the highest recorded, being 62 x 198-230-1- 

 198-230. Nor are any striking differences to be found in the form and size of 

 the individual teeth in these species. The median one is small and incon- 

 spicuous, with its hook small, rudimentary, or absent {D. calif ornica). Eliot 

 states that the median tooth is entirely wanting in D. hasseltii from Samoa, 

 but in my serial sections of the pharyngeal bulb of a specimen of this species 

 from the same locahty I have no difficulty in recognizing it as a flattened plate 

 bearing a small hook, so his observation is probably erroneous. Nor do I find 

 any such compUcated forms of teeth as those figured by MazzarelU and Zuccardi 

 (1890, tav. 1, fig. 16, 18-20), and am inchned to question their interpretation 

 of the microscopic appearance of the teeth, which, as is well known, is often by 

 no means an easy matter. The statement of Bergh that the median hook of 

 D. scapula is finely denticulate is not confirmed by Vayssiere nor by Farran. 

 The lateral teeth are uniformly simple compressed hooks of regular form and of 

 fairly uniform size, the dentition as a whole thus differing widely from the 

 type characteristic of all other genera of the Aplysiidae, in which strongly 

 developed median and lateral teeth with comphcated denticulations are found 

 in every species. With what this striking difference may be correlated is not 

 evident, in the lack of any information as to food, habits, etc. 



Palatal folds. — The postero-dorsal region of the pharyngeal bulb, directly 

 overlying the radula, bears a pair of flap-Uke reduplications of the dorsal wall, 

 which project obUquely downward and backward into the cavity (Plate 8, 

 fig. 5, l.f.). These folds are of an elongated triangular form, the pointed apex 

 being directed forward, while the posterior free end is rounded and lobe-like. 

 They are continuous with the dorsal wall of the bulb along their outer margins, 



