PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 



549 



supposition that the genus had its origin in Antarctica, or one of the 

 Austral lands once connected therewith. 



Littoridina resembles the Holarctic Paludestrina and the genus Fluvio- 

 pupa 1 of Australia and the Melanesian Plateau, but until the external 

 genitalia of all can be compared, no well-founded opinion of the affinities 

 of these genera can be formed. 



Idiopyrgus is an Archhelenic genus, if my estimate of its affinities is 

 correct. 



The affinities of Lithococcus are uncertain. 



Potamolithus, in the form of the shell, closely resembles the genera 

 assembled by Tryon in the subfamily Lithoglyphina : Fluminicola of 

 western North America, Lithoglyphus of eastern Europe, Pachydrobia, 

 Lacunopsis and Jullienia of Indo-China. All of these genera differ from 

 Potamolithus by the small number and large size of the cusps of the outer 

 marginal teeth. 2 Fluminicola has male genitalia of widely different form. 

 The genus Petterdiana of Tasmania and Australia has a strong globular 



FIG. 6. 



Petterdiana tasmanica (Tenison-Woods), half row of teeth and an isolated outer marginal tooth. 



shell, with wide columella, similar to the primitive species of Potamolithus. 

 The radula, hitherto undescribed, has the formula ^. 2, i, 5. 20. 25 

 (Fig. 6, teeth of a half row, and a detached outer marginal tooth). This 



1 Fluviopupa n. gen., type F. pupoidea (Mousson) of Fiji. The teeth are of the usual shape in 

 Amnicolinee, central with the cusp formula V^f admedian with 10 subequal cusps, marginals 

 with about 30, those of the outer marginal very minute. Shell pupiform, with obtuse summit 

 and convex sides, the aperture ovate, vertical or sloping forward below, the long parietal margin 

 straightened. Operculum thin, with nucleus near the base. Penis unknown. Hydrobia pttttfdt 

 E. A. Smith seems to be congeneric, judging from specimens sent from Manaro, N. S. Wales, 

 by Dr. J. C. Cox. These shells have the appearance of the European Bythinclla, but differ 

 from them in dentition. 



2 See J. Poirer, Journal de Conchyliologie, XXIX, 1881, pp. 1-19. 



