1905.] NATURAL SCIENCES OF PHILADELPHIA. 711 



ZONITID^. 



The Zonitidce of the Ogasawara or Bonin Islands, exclusive of Hi- 

 rasea and related forms, may be determined by the following key. The 

 generic relations of part of the forms are uncertain, since we as yet 

 know little of the extent to which convergent evolution has moulded 

 shell-form in this family. 



I. — Shell elevated, trochiform, as high as wide, 5x5 mm.; whorls 7^, 

 the last strongly angular,. . . . Kaliella ogasawarana Pils. 

 II. — Shell depressed, the spire convex or low-conic. 

 a. — Columella thin, reflexed. 



b. — Very glossy and densely striate spirally above and below; 

 periphery not carinate, obtusely subangular. 

 c. — Shell narrowly, obliquely perforate; 3x4.5 mm., 



Macrochlamys chaunax. 

 C-. — Shell narrowly umbilicate; 2x3.2 mm., 



Macrochlamys lineatus. 

 b^. — Periphery strongly carinate. 



c. — Surface dull, minutely, irregularly granulate, 



Otesia chichijimana. 

 c\ — Surface glossy, obliquely wrinkled and spirally, 



striate, 0. hahajimana. 



a^. — Columella calloused within, with a low tooth or nodule. 

 Spiral strise wanting or excessively faint, Microcystina. 

 b. — Periphery rounded, or very weakly subangular in front; 

 surface very glossy. 

 c. — Outer lip thin; whorls 5; about 4 x 6.5 mm., 



Microcystina hahajimana Pils . , 1 902 . 

 c^ — Outer lip thin; whorls about 4f ; smaller, about 2.9 x 



5 mm., M . hahajimana jejuna. 



(?. — Outer lip thickened within; whorls 4^; 2.8 x 5 mm., 



M. hahajimana pachychilus. 

 c'. — Outer lip thin; spire quite convex; aperture a nar- 

 rower crescent; whorls 4^; about 2.7 x 4 mm., 



M. hahajimana kitaiwojimana. 



¥. — Periphery with an inconspicuous but rather acute angle 



in front, elsewhere rounded ; whorls 4^; 2.2x4 mm., 



M. anijimana. 



Microcystina hahajimana Pils. 



This species was described in 1902 from specimens from Hahajima 

 Ogasawara, the types being 82,606, A. N. S. Phila., No. 803 of Mr. 

 Hirase's collection. It seems to be a typical Microcystina, having a 

 calloused, obtusely nodular columella, and a glossy surface which is 

 not spirally engraved. Numerous closely related forms have subse- 

 quently been received from various islands, as follows: 



