ox SOME CRETACEOUS FOSSILS FKOM SHIKOKU. oÜ 1 



Description of the Species. 



Trigonia pocilliformis H.sp. 



VI XL, Fig. la, 11), 2, 3. 



Tr'ninida sj>. Yokoyama, Vei-steincruugeu ans tier Japaiiisclieu Kreide, p. 19'J. 



Shell subcrescentic, very iiiequilateial, iuflated auteriorlv, at- 

 tenuated, iiarroAved, aiid tiattened powteiiorly. 1 leaks autero-iiiesial 

 tuuchiuu', pointed, much incurved and also recur\ed. The anterior 

 side of the valve is somewhat pr«xluced, and its margin is stron^'ly 

 convex, gradually passing int() the convex ventral margin which is 

 raised up posteriorly without any marked excavatitjn. The dorsid 

 margin commences at the small ligamental a[)erture behind the beak, 

 and descends posteriorly with a slight concavity to meet the truncated 

 siphonal margin nearly at a right angle. The escutcheon is lengthen- 

 ed, ovato-lanceolate when the valves are closed, broadest at about y., the 

 distance from the beak, and concave for about -/-^ the length from the 

 same point, beyond which it liattens. It is transversely or somewhat 

 obliquely costellated : the costellai are sim])le and smooth, beinf- 

 coarser, more elevated and distant in the p<jsterior than in the anterior 

 ])(jrti(3n of the escutcheon. They are also sliglitlv curved out towards 

 the posterior side, and somewhat oblicpie, with the marginal ends 

 directed anteriorly. The number of these costella' is probably 15-18, 

 but those situated near the beak p.re so fiint that thev are hardly 

 visible. The area begins near the beak as a slight ridge which 

 gradually widens posteriorly and l^ecomes broadest at the siphonal end, 

 where it attains about 7^ the total heiglit of the shell, and forms at the 

 same time its posteriijr boi-der. It is for the greater part of its length 

 rendered bipartite Ijy a groove which runs a little above its median 



