184 Avt. 6.— M. Yokoyaraa : 



The mumber of riblets may be generally taken at about sixty 

 at the anterior margin, though in a small specimen 15 millim. in 

 length, only fifty have been counted. 



A species which most resembles this one is Terebratidina caput 

 serpentis var unguiculata Da v. (1. c. p. 25, pi. v, figs. 38-40) from 

 which the Japanese fossil differs in being generally broader, with 

 the broadest part somewhat posterior to the middle of the shell. 



Rather frequent, but mostly distorted. 



Fossil occurrence. — Koshiba Zone (Koshiba). 



Genus Terehrafelta* d'Orbignv. 



236. Terebratella coreanica, (Adams et Reeve). 



Pl. XIX. Figs. 25, 28. 



Terebratella coreanica. Davidson, Monogr. Bee. Brach., p. 81, pl. XIII, figs, 3-9. Dall, 

 Airier. Jour. Conch., vol. VI, p. 121. Dunkeb, Index Moll., p. 252. Pilsbry, Cat. Moll. Jap., 

 p. 151. 



Terebratitla coreanica. Adams and Reevp, Voy. Samarang, p. 71. pl, XXI, fig. 3. Schrenck, 

 Moll. Amurl. u. d. nordjap. Meeres, p. 168. Lischke, Jap, Meeresconch., vol. I, p. 181. 



There arc two specimens. The one (fig. 28) has the shell 

 large, longitudinally oval, swollen, longer than wider, widest about 

 the middle. The dorsal and ventral valves are unequally convex, 

 the dorsal valve being less convex than the ventral; the convexity 

 of the dorsal valve is uniform and flattish, except near the anterior 

 margin where it is very slight; the ventral valve has a strong 

 longitudinal fold which, without any distinct boundaries, slopes to, 

 and passess into, the lateral sides. Beak of ventral valve 

 incurved, obliquely truncated b}^ a large foramen, incompletely 

 bordered in front by a separate deltidium. Surface smooth, only 

 with lines of growth. Shell-structure finely punctate. Length 

 45 millim., breadth 40 millim., thickness 2o millim. It is no 

 doubt an elongated form of the species above mentioned which is 

 remarkably variable in shape. 



The other (fig. 25) is a somewhat imperfect specimen with 

 the ventral valve firmly attached to a stone, while the dorsal 

 valve has fortunately been isolated from the same. It is a roundly 

 pentagonal variety. The dorsal valve is nearly 30 millim. in 



