128 OPEAS GRACILE. 



lar margin is widely reflexed. Two specimens from Ahmed- 

 nuggur measure: 



Length 12, diam. 3.5, aperture 3.8 mm., whorls 8^2- 



Length 13, diam. 3.1, aperture 3.7 mm., whorls 9. 



These shells (pi. 18, figs. 3-5) illustrate the slender and 

 stouter phases of the species, usually to be found in any 

 large lot from one place. 



The series before me from Mauritius, Ceylon, India, China, 

 the Philippines, etc., shows but little variation except in size. 



Specimens from Okinawa, Ryukyu, have slightly more 

 convex whorls, the striation is a trifle weaker and they are 

 more glossy (pi. 18, fig. 6), the one figured measuring 12.8 

 x 3.5 mm., with 8y 2 whorls. Further north 0. gracile has 

 been found by Mr. Hirase in Kyushu, Hondo and even as far 

 as Kayabe, Ojima, in the island of Yesso further north 

 than any other species of the genus. A shell from this place 

 measures 11.3 x 3 mm., with 9 whorls. It has been found 

 by Mr. Hirase 's collector on Kita-iwojima, one of the Sulphur 

 group, near the Bonin Islands, and on Hahajima, Ogasa- 

 wara (Bonin Is.) ; the form occurring there (pi. 22, fig. 10) 

 being small, 8 mm. long, with 7 whorls, the suture subtly 

 crenulate in places. It is thin and delicate, as might be ex- 

 pected on volcanic soil. 



The Chinese Bui. fortunei Pfr. and "B. scalaris Desh." 

 have been considered synomyms of 0. subula Pfr. by Gredler. 

 The former is placed in the synomyms of Bui. decorticatus 

 Reeve by von Martens. I have not the material for decid- 

 ing this question. See page 34. Bulimus cereus Reeve (pi. 

 18, fig. 7) was based on an Indian specimen of gracile. 



The following form from the Nicobar Islands is apparently 

 synonymous. il Opeas apex Mouss., var. nico~barica. Shell 

 narrowly turrited, waxen outside, white within, with 7% 

 quite convex whorls, the first two smooth, yellow, the rest 

 irregular, costulate-striate, the riblets obsoletely sigmoid, es- 

 pecially on the last whorl, and with very obsolete spiral lines, 

 stronger on the base. Suture deep, subcrenate, more dis- 

 tinctly so in the middle whorls. Aperture subelliptical, some- 

 what narrow anteriorly, inner lip reflexed, with a very obso- 



