1(50 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



The jaw (PI. XVI, Fig. 3) is well arched, thin, with its lower 

 margin crenulated by the termination of thirteen, or fourteen flat 

 'ribs,' which seem separated by narrow intervals in the median 

 part, contiguous or slightly overlapping towards the ends. It is just 

 such a jaw as exhibited by some species of Papuina intermediate 

 between the plaited and ribbed types. 



Dimensions of the Pallial Organs, in millimetres. 



From the foregoing it will be seen that the three species investigated 

 agree in all important characters, while differing in various minor 

 points. Compared with Amphidromus (s.s.), the subgenus Beddomea 

 agrees in external characters, the long, band-like kidney, the pattern 

 of lung reticulation, the arrangement of muscles (except as noticed 

 below), the entire reproductive system, and the jaw. I have also 

 been unable to find any differences between the central nervous 

 system of Amphidromus intermedins and Amphidromus as figured by 

 Wiegmann. 



Beddomea differs from Amphidromus (1) in having the right ocular 

 retractor passing to the right of both branches of the genitalia, not 

 between them: (2) in having the cusps of the teeth on the median 

 field of the radula broadly rounded and simple, instead of deeply 

 cloven into onto-, meso-, and ecto-cones, as all the laterals are in 

 Amphidromus ; the marginal teeth of Beddomea, however, are cloven, 

 and like those of Amphidromus ; they also resemble the marginals 

 in Papuina : (3) in having the radula longer in proportion to its 

 breadth than it is in Amphidromus. 



In view of the general agreement, it scarcely seems well-advised to 

 accord Beddomea higher rank than that of a subgenus of Amphidromus. 

 None of the three structural differences mentioned is of much 

 importance, though I do not doubt that they will prove constant in 

 Beddomea. When some of the species of Amphidromus which are 

 conchologically nearest Beddomea (such as A. sylhetieus) come to be 

 examined, transitions may not unlikely be found in the dentition. 



1 The specimen of A. albizonatus was rather small, though mature ; length of shell, 

 25 mm. A larger individual would, of course, give increased dimensions for 

 the organs, without changing their proportions. 



