FOSSILS FKOM THE ENVIRONS OF T(JKY0. 61 



the posterior Im It' of the dorsal margin is also niueh produced 

 and straight, giving a distinctly truncated shape at the posterior 

 Hide. Tlie uni bones are sunken at the middle. It may however 

 be a young form of some other species of Area. 



150. AR( A RECTANGULARIS Tok. 

 PI. III. Figs. 23 a, b and c. 



Shell subquadrate, gaping anteriorly and posteriorly; anterior 

 side short, distinctly trujicate, the posterior surface of the shell 

 distinctly marked off from the anterior ; dorsal side almost 

 straight, angulate at the a ntero- dorsal margin ; ventral margin 

 curved in the middle ; surface with fine granulated radial ribs ; 

 hinge linear, straight, formed of a large number of small pecti- 

 nated teeth; ligament external, attached on a very broad lozenge- 

 shaped area between the beaks ; beaks high, rather wide apart. 

 Length 15"""; height 7"'"'; breadth ll.o""". 



Our species differs slightly from A. navicularis Brug. found 

 in the Indian Ocean and the Philippines by its thicker shell 

 and more numerous ribs in the anterior part. A. noce Linn. 

 differs from ours, firstly, in its size and in the shape of the 

 posterior side, secondly in having more than thirty ribs without 

 intermediate riblets, and thirdly in the form of the posterior 

 portion of the internal surface. A. maculata Rye. much re- 

 sembles the Japanese species, but its antero-dorsal margin is 

 almost rectangularly truncated. 



Shinagawa (very rare). 



The living specimens were collected at Hakodate. 



151. PECTUNCULUS ALBO-LINEATUS Lischke. 



Brauns, Geol. Env. Tokio, p. 45. — Wood, Crag IMoll., II., p. 66, 

 and suppl. p. 43. — LiscfiKi:, Jap. oMeeres-Conch., III., p. 108. 



