26 Art. 6. — M. Yokoyarna : 



DESCRIPTION OF THE SPECIES. 



Subkingdom Mollusca. 



Class Gastropoda. 



Order Opisthobranchiata. 



Family Tornatinidae. 



Genus ßetusa, Buown. 



1. Retusa minima, Yamakawa. 



Pl. I. Fig. 1. 



Retusa minima. Yamakawa, Descript. of Some Foss. Opisthobrancriiata fr. Diluv. Dep. of 

 Japan, Jour. Geol. Sec. Tokyo, vol. XVIII, No. 212, May, 1911, p. 47, pl. XI, figs. 21-24. 



We possess two specimens which can be identified with the 

 above-named species which Yamakawa characterized as follows: — 



"Shell small, thin, cylindrical, somewhat compressed in the 

 middle; upper end depressed, concave, retuse, with a plicated 

 nucleus in the centre of the bottom; lower end obtuse; suture 

 deep; whorls four, flattened; surface smooth, only with many fine 

 obtuse longitudinal growth-lines; aperture as long as the shell, 

 narrow, linear, with the lower one-third abruptly expanded; 

 pillar-lip with an obtuse fold; cuter lip curved forward in the 

 middle. Height 3 millim. Diam. 1.5 millim." 



One of our specimens measures 2,5 millim. in length and 1,2 

 millim. in thickness; while the other measures 2 millim. in length 

 and 1 millim. in thickness. 



Fossil occurrence: — Miyata Zone (Okine in Nagai); Naga- 

 numa Zone (Naganuma); Upper Musashino of Musashi, Shimosa 

 and Kazusa. 



Genus Volvtila, A. Adams. 

 2. Volvula acuminata, (Brtjguièbe . 



Pl. I. Fig. 2. 



Volvula acuminata. Tbyon. Man. Conch., vol. XV, p. 236, pl. XXVI, figs. 61, 62, pl. LX, 

 fig. 11 (var. brevis). 



Volvula acuta. Tokunaga, Foss. Env. Tokyo, \>. 32, pl. n, fig. 13. 



Bulla acuminata. Bruguière, Encycl. Méth., I, p. 376. Philippi, Ennm. Moll. Sicil., I, p. 

 122, pl. VII, fig. 1. Wood, Crag Moll. I, p. 174. pl. XXI, fig. 7. 



Cylichna acuminata. Jeffreys, Brit. Moll. IV, p. 141, V, p. 222, pl. 93, fig. 1. 



