•] \)Q Art. 1. — M. Yokoyama : 



Isl, Proc. Zool. Soc. Lond., 188G, p. 570, pi. XXVIII, fig. 19. Pilsbry, Cat., p. 

 1;jO. Yokoyama, Foss. Miura Penin., p. 168, pi. XVIII, figs. 1, 2. 



The characteristic feature of this shell usually consists in the 

 postero-dorsal margin heing a little longer than the antero-dorsai, 

 whereby the rounded or, as is sometimes the case, subangulate 

 corner between the former and the posterior margin becomes more 

 or less conspicuous. But it is here to be remarked that this chara- 

 cter is not always obvious, especially in young specimens, so that 

 the distinction from Pectu7iculus vestitus sometimes becomes very 

 difficult, or even impossible. 



The largest specimen obtained measures 65 millim. both in 

 length and height. 



Fossil occurrence. — Otake (frequent), Shisui, Kioroshi, Tega, 

 Kamejiari, Shito (very common). Lower Musashino of Mij'ata. 



Living. — Northern Japan. 



31S. Pectunei€lM€s pilshryi, Yokoyauia. 

 PI. XVI. Figs. 8, 9. 

 Pectunculits jnlsbfiji. Yokoyama, Foss. Miura Penin., p. 170, pi. XVIII_, fig. 8. 



This small oblique Pectunculus is generally characterized hj 

 the subangulate posterior end and the fine, close, unequal, radia- 

 ting riblets which cover the whole surface. The posterior end, 

 however, may sometimes be subtruncate or so produced as to 

 assume a rostrate appearance as shown in the figure. The granulate 

 nature of the riblets are not alwaj^s distinct. 



The largest example attains a length of 'lb millim. and a 

 height of 23 millim. The depth of a valve of such specimens is 

 about 7 millim. 



Fossil occurrence. — Shito (very common). Lower Musashino 

 of Miyata (rare). 



Living. — Central Japan. 



319. Peetunculus yatiiuhatvai, Yokoyama. 

 PI. XVI. Figs. 4, 5. 



A right and a left valve. Both are flattened (right valve being 

 30.5 millim. long, 28 millim. high and 6 millim. deep), oblique 



