106 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



which occupies the usual position on the right side of the pulmonary 

 sac, is entirely surrounded by a large blood-sinus, from which afferent 

 vessels are distributed to the roof of the pulmonary chamber. The 

 liver (r.l. and 1. 1.) is divided into right and left lobes, the former 

 enclosing the ovotestis ; the latter is subdivided into three lobules, 

 each of wbich contributes a bile-duct, the three main ducts opening 

 into the left side of the stomach by a single aperture. 



Radula. — The radulae of three species of Acavus have already been 

 figured, viz., A. hcemadomus by Pilsbry, 1 A. phoenix by Binney, 2 and 

 A. Skinneri by Semper 3 ; since, however, only two or three teeth, 

 at the most, have been represented, I have thought it advisable to 

 refigure them for the purpose of comparison with the radulae of the 

 remaining species of this genus. 



The teeth are unicuspid, only the mesocono being represented. No 

 trace of either ectocone or entocone is visible in any of the teeth, 

 the extreme laterals possessing only a single cusp. The radula of on 

 embryo of A. phoenix taken from the egg exhibited no trace of the 

 tricuspid condition in either lateral or marginal teeth, and differed 

 from the radula of the adult only in the size and number of the teeth. 



So slight are the differences in the radulae of the various species 

 of Acavus, that an examination of the figures (PI. IX, Figs. 2—7) will 

 give a much clearer idea of the specific peculiarities than any detailed 

 description. 



Individual variation in the number of teeth in a transverse row 

 of the radula appears to be a common feature in all the species, 

 though, so far as I can judge from the examination of the radulae 

 of a limited number of specimens of most of the species, this variation 

 in number would seem to lie within certain bounds. 



In A. hcemasiomus (PI. IX, Fig. 2) the central or rhachidian tooth 

 is long and narrow, the reflexed portion and cusp being stout and 

 projecting considerably beyond the middle of the tooth. The 

 admedian teeth are provided on their inner (mesial) border with 

 a rounded projection of the upper margin of the base of attachment, 

 which fits into a concavity on the outer border of the preceding tooth. 

 This process is larger and more distinct in some individuals than 

 others. In addition there is a projection on the base of the tooth, 

 against which the head of the corresponding tooth on the subsequent 

 row abuts. The base of attachment of the lateral teeth gradually 

 becomes smaller, and the cusp relatively longer, the further the 

 tooth is situated from the middle line. In the marginal teeth this 

 diminution of the base becomes even more marked, whilst there is 

 a tendency for the reduction of the cusp in the extreme marginals, 

 culminating in the entire absence of a cusp in the last two or three 



1 Manual of Conchology, ser. n. vol. ix (1894), p. 153, pi. xlviii, fig. 14. 



2 "Notes on the Jaw and Lingual Dentition of Pulmonate Molluscs" : Ann. New 



York Acad. Sci., vol. iii (1883-5), p. 92, pi. ii, fig. Q. 



3 " Reisen im Archipel der Pliilippinen," Tkeil ii, Bd. iii, Land-mollusken (1870), 



pi. xvi, fig. 5. 



