4.0 MIT. J. II. YABE : CllETACEOUS 



1) A specimen from the Opiniusliil)ets, Prov. Tesliio. 



2) \ spécimen from the Ynbarigawa, Prov. Ishikari. 



►Shell thick, discoidal, con) posed of many whorls ; whorls some- 

 what trapezoidal being laterally flattened, ventrally inflated and 

 slightly broader than high. Umbilicus narrow, deep, with a 

 perpendicular wall and ])luntly angular edge. Involution about 

 i. Surface with verv fine but distinct stride of irrowth, without 

 any trace of periodic ribs. The older specimens show whorls more 

 rapidly increasing in height and Ijreadth, and ])rovided with peri- 

 odic ribs. These ribs are slightly elevated and rounded, correspond- 

 ing to shallow furrows on the cast of the interior. They are 

 wddely separated, there being only two or three in one volution. 

 The fine strite as well as the periodic ribs which are also covered 

 with striie, rise at the umbilical suture, l)end obliquely forward 

 on the lateral sides and then backward on the ventral side. 

 Besides there are a few longitudinal lines on the external half 

 of the lateral sides which are visil)le only on the last half of a 

 volution of the largest specimen in the writer's collection. The 

 periodic ribs begin to ap})ear when the shell attains 7 cm. in 

 diameter. 



The length of the body chandjer of Teiragoniics is not yet 

 known. The largest specimen, mentioned above, shows two thirds 

 of the last volution not septate, but as the anterior end of the 

 whorl is broken off, the length of the body chandjer nuist l^e 

 more then 5 of a volution. 



Suture line as in the preceding species. 



There are many well })reserved individuals of this species in 

 the writer's collection, one of which is shown in fig. 1, PI. VII. 

 The al;)ove diagnosis was written after a study of them and the 

 two specimens in Jindjo's description essentially agree with them. 



