J40 '^^'^- ^- — ^- Yokoyama: 



This thin-shelled species already described by Branns and 

 Tokunaga from the environs of Tokyo and by me from the Lower 

 Mnsashino of the Miura Peninsula is very frequent at some places. 



Fossil occurrence. — Otake (frequent), Kamenari, Shisui 

 (frequent), Tega, Shito (very frequent). Oji and Shinagawa in 

 Musashi. Lower Musashino of Miyata and Naganuma. 



Living. — Central and Western Japan. 



316. Tellina altefufita, Say rfir. ehihaiKi, Yokoyama. 

 PI. X. Tigs. 5, 6. 



Shell rather thin, compressed, transversely elongated, almost 

 twice as long as high, a little inequilateral with posterior side 

 somewhat shorter tlian anterior, rounded in front, obliquely 

 subtruncate behind. Antero-and postero-dorsal margins nearly 

 straight; ventral margin broadly arched. Surface concentricallj^ 

 grooved; grooves rather fine, pretty regular, although often 

 indistinct through friction. Also fine discontinuous and irregular 

 radiating lines present. A keel runs from the beak to the 

 postero-ventral corner, behind which there is a very shallow 

 depression. Palliai sinus large, deep and oblong. Anterior main 

 tooth in left valve and posterior main tooth in right valve Ijifid. 

 Lateral teeth two, one in front and one behind. Rather frequent. 



The largest example is a right valve measuring 49.4 millim. in 

 length, 26.6 millim. in height and 4.8 millim. in depth. The 

 largest left measures 45.4 millim. in length, 27 millim. in height 

 and 4.5 millim. in depth. 



This shell still living near our coast agrees quite well with 

 Tellina alternata Say (Philippi, Abbild., vol. II, p. 23, pi. Ill, 

 fig. 1 and Syst. Conch. Cab., Tellina, pi. XXV, figs. 10-15) from 

 the east coast of the United States in form, the only dilïerence 

 being the shallower palliai sinus and the absence of radiating lines 

 in the latter. Therefore I deem it expedient to treat the Japanese 

 form as a variety of the American. 



Fossil occurrence, — Otake, Kamenari, Shito. 

 - Living. — Central Japan. 



