162 PROCEEDINGS OF TUE MALACOLOGICAL SOCIETY. 



The jaw and dentition of Amphidromus resemble those of certain 

 forms of Papuina; though as I have shown in the "Guide to the 

 Study of Helices," all arboreal Helices tend to form broad, gouge-like 

 cusps to the teeth, either by enlargement of the middle cusp of each 

 tooth or of all three cusps ; and arboreal genera of demonstrably 

 diverse ancestry sometimes converge towards a common type of 

 dentition. For this reason, mere similarity of teeth is not necessarily 

 a proof of genetic relationship. 



Enough has been said to show that Amphidromus has no affinity 

 to the Bulimulidse or the ' Bulimi ' of either hemisphere. It is 

 unquestionably a member of that division of the Helicidae which 

 I characterized as the Epiphallogona, or Cammnince ; and it differs 

 from such well-known genera as Chloritis, Thersites, and Papuina in 

 very little besides the elongated shell. In conchological features, 

 however, it is strongly differentiated and individualized. 



EXPLANATION OF PLATE XVI. 



Fig. 1. Retractor muscles of Amphidromus albizonatus. ph.r. retractor of the 

 pharynx ; p.r. pedal retractors ; r.o.r. right ocular retractor ; t.r. tail 

 retractor or columellar muscle (spirally coiled). 



,, 2. Genitalia of A. intermedins, epi. epiphallus ; Jl. flagellum. 



,, la. Distal eud of penis of same, opened to show the papilla. 



,, 3. Jaw of A. Oeylanieus. 



,, 4. Outline of radula of A. intermedins, with a single row of teeth indicated. 



,, 5. Genitalia of A. albizonatus. 



,, 6. Pallial organs of A. intermedins, k. kidney ; u. ureter. 



,, 7. Teeth of A. intermedins. Groups from the median, transition, and lateral 

 portions of the radula. 



Note. — Figures 1, 2, 5, and 6 are twice the natural size ; the others magnified in 

 various degrees. 



