46 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



7. Gastropoda. 



Peculiar Venezuelan Land Snail. — "Henry A. Pilsbry {Proc. 

 Acad. Nat. Sci. Philadelphia, 1919, 71, 206, 1 fig.). A minute discoidal 

 shell, concave above and below, whitish-transparent, glossy, with 

 sculpturing of spaced radial grooves after the first half whorl. These 

 grooves become closer near the aperture, and in the largest and freshest 

 specimens they are occupied there by projecting riblets, which may be 

 partly cuticular and deciduous. The specimens were 0'55 mm. high 

 and 1*6 mm. in diameter, and were obtained by sifting leaf debris. 

 The affinities remain uncertain, as it is very unlike any described form. 

 It doubtless belongs to a new genus, provisionally placed near Proserpinida 





Three views of Xenodiscula venezuelensis, and the aperture 

 more enlarged. 



or Volvidens, both Antillean genera. The name proposed is Xe?iodiscida 

 venezuelensis g. et sp. n. J. A. T. 



Gastropods of Old Lake-heds in Upper Burma. — Nelson 

 Annandale {Records Geol. Survey India, 1919, 50, 209-40, 3 pis.). 

 Attention is called to parallel evolution or convergence on a large scale 

 in the shells of fresh-water Gastropods of different regions and epochs. 

 The evolution of the genus Taia, a peculiar off-shoot of the Yiviparidfe, 

 with peculiarly ridged, nodulose, and even spiny shells, is exactly parallel 

 i% but quite independent of, that which produced Margarya in the 

 lakes of south-western China, and also that which, at an earlier period 

 and in a distant country, resulted in a large series of species of 

 Vivipara and Tulotoma with a similar type of shell in the Vienna basin. 

 But Taia is proved by the peculiar structure of its columellar callus to 

 be only analogous, not homologous, with the Austrian and Chinese 

 forms. The genus Vivipara has, in fact, again and again, in diverse 

 countries and at different periods, manifested, when left undisturbed 

 and isolated for longer periods, a tendency to produce shells ornamented 

 with smooth spiral ridges. With further evolution these ridges become 

 at first undulated on the surface, then granular or nodular, and finally 



