298 ME. GUY C. EOBSON ON MOLLUSCA 



systematic position. Increase in our knowledge of the anatomy of the group or of the 

 conchological forms assigned to the group only can render the work possible. The 

 following instance may serve as an example of the importance of anatomical work in 

 dealing with such a group : — The conchological differences between the present species 

 and many of the shells of the genus Dendrotroclius, now recognized as a Zonitid, are 

 insignificant ; and, moreover, the Zonitid forms more closely resemble this species of 

 Paimina than do typical species of Papuina. Further, if it were to be maintained 

 that the conchological characters that differentiate this species (and with it the other 

 thin fragile Papuinas) from, e. g., Dendrotroclius heUcinoides, are of family value, then 

 it may be pointed out that such a reasoning would compel us to put such forms as 

 P. hoivini and P. wollasioni, not to mention other well-founded species of Papuina 

 which differ markedly on conchological characters, into separate families ! 



There are a number of other species oi Papuina conchologically near this form, but 

 which, in default of anatomical knowledge, we must hesitate before grouping with it. 

 These are : — P. molcsta Smith, P. leucotropis Pfr., and P. arrowensis le Guill. 



A. External Appearance. 



The animal was very much shrunken by the spirit in which it was preserved. 



Upon removing the shell the first thing that attracts attention is the pigment-tracts 

 on the dorsal surface of the mantle (PL XXXIII. fig. 2). The intestine is seen in the 

 usual position, and the integument covering it, as far as it can be traced, bears 

 at regular intervals a number of dark brown patches, from each of which radiate a 

 number of streaks, which run to the mid-dorsal line to form a faint irregular band in 

 that axis or anastomose with similar lines from the patches anterior and posterior to it. 



These pigment-tracts are in no way connected with the vascular system, the vessels 

 of which may be seen running in no correspondence with the pigment, which lies in 

 loose, rather superficial accumulations. The proximity of the centres of radiation to 

 the intestine suggests that this pigment may be a digestive product. Kiikenthal's 

 description of the mantle of P. vitrea (7) as "dunkelbraun marmoriert und getigert " 

 shows that other Papuinas are similarly decorated in a manner that may express 

 specific differences. 



A diagrammatic representation of the pattern in this form is given (PI. XXXIII. 

 fig. 2 h). 



The foot-sole is narrow, undivided, and somewhat expanded posteriorly into a 

 spatulate shape. The colour of the foot is light brown. 



The shell (PL XXXIII. fig. 9 a, b, c) is delicate, acutely carinate, and lenticular in 

 general appearance, the apex being somewhat depressed. The upper half exceeds the 

 lower by very little in size. Whorls 4~. The surface is sculptured by faint irregular 

 lines of growth crossed by very fine and delicate spiral lines, which are usually undu- 

 lating, and is, in addition, broken by bristle-scars arranged in a rudely quincuncial 



