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 Vayssiére (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 (Vayssiére), 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. californica). 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 locality 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 complicated forms of teeth as those figured by Mazzarelli and Zuceardi 
(1890, tav. 1, fig. 16, 18-20), and am inclined 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 Vayssiére 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 complicated 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, ete. ‘ 
Palatal folds— The postero-dorsal region of the pharyngeal bulb, directly 
overlying the radula, bears a pair of flap-like reduplications of the dorsal wall, 
which project obliquely downward and backward into the cavity (Plate 8, 
fig. 5, l. f.). These folds are of an elongated triangular form, the pointed ap 
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 margi 
