1902.] NATURAL SCIENCES OF PHILADELPHIA. 121 



Simoda (or Shimoda) is at the southern end of the Izu peninsula and 

 ' ' Ousima ' ' is Oshima, a large island northeast of Okinawa, in the 

 " Riukiu Curve." There is also an Oshima (Izu-no-Oshima) at 

 the mouth of the Sagami Sea, one of the ' ' Seven Islands of Izu. ' ' 

 The name, meaning " big island," is somewhat common in Japan. 

 M. retifera Tryon is a rather small form of libertina, with some- 

 what coarse spirals but no folds. M. hakodadiensis Hartman is 

 normal libertina with even and rather fine spirals. The types of 

 both are before me. M. boninensis Lea, of which two of the origi- 

 nal lot, given by Lea, and several collected by Mr. S. Yoshiwara, 

 lie before me, is a dwarfed island form of the libertina stock, dis- 

 tinct by its small size and somewhat attenuated contour. It has 

 erroneously been referred to a separate section of the genus by 

 some authors. 



AMNICOLIDJE. 



Bithynia striatula var. japonica Pilsbry. PI. IX, figs. 9, 10, 11, 12. 

 These Proceedings for 1901, p. 405. 



Figs. 9, 10, 11 are from specimens of the type lot, from 

 'Manabe, Hidachi. Fig. 12 is the smoothest specimen of a series 

 from Osaka. 



The operculum has a distinctly spiral nucleus in this species. 

 This feature has twice been made the basis of generic distinction, 

 but I prefer to retain the species in Bithynia until a thorough study 

 can be made of the opercula of the group. Probably several stocks 

 have independently changed from the spiral to the concentric type. * 



EXPLANATION OF PLATE IX 



Fig. 1. Vimparus japonicus v. Mart. Omaki, Yamashiro. 

 Fig. 2. Melania hidachiemis Pils. Manabe, Hidachi. 

 Fig. 3. Vimparus japonicus var. Iwakawa Pils. Furukawa, Rikuzen. 

 Fig. 4. Vimparus sclateri Ffld. Near Kyoto. 

 Fig. 5. Vimparus histricus Gld. Kagoshima, Satsuma. 

 Fig. 6. Vimparus malleatus Rve. Kagoshiraa, Satsuma. 

 Fig. 7. Vimparus malleatus Rve. Okinawa, Riukiu Islands. 

 Fig. 8. Melania libertina var. latifusus Pils. Mino, Settsu. 

 Figs. 9, 10, 11. Bithynia striatula var. japonica Pils. Manabe, 

 Hidachi. 

 Fig. 12. Bithynia siriatula var. japonica Pils. Osaka. 



4 Dr. O. von Mollendorff has referred B. striatula to the genus Fossa- 

 rulus Neuinayr, and has discussed the status of Pere Heude's Chinese 

 species in a paper which caine to hand since the above was written. 

 Annuaire du Musee Zoologique de I' Academic Imperiale des Sciences de 

 St. Petersbourg, VI, 1901, Binnen-niollusken aus West-china und Central- 

 asien, p. 101 (1902). 



