(hi) 18 Palxontoloijia Sinica Ser.B. 



This species is longitudinally ovate, much higher than wide. The hinge 

 line is a little shorter than the greatest width which lies just below the median 

 line of the shell. The pedicle valve is uniformly convex and rather strongly arched. 

 The beak is moderately protuberant and a little incurved. The surface orna- 

 mentation consists of round plications which bifurcate into smaller and secondary 

 plications at varying distances from the beak. Because of this feature the inter- 

 spaces are very narrow. There are on the average eight plicae in five mm. at the 

 front. 



Remarks: This species agrees well with Davidson's description of Orthis 

 elegantula. It differs from Orthis testudinai^ia Dalman in being higher than wide, 

 while in the case of the latter the reverse is usually true. 



Horizon and Locality: Occurs with the preceding. Coll. C. C. Yii. (Ser. 

 Nos. X 213, X 236; Cat. Nos. 3387, 3388). 



Genus RafINESQUINA Hall and Clarke 



14. Raflnesquina cf. muthensis Reed 



PI. II, Figs, iia-b. i2a-b. & i3a-b. 

 cf. 1912. Rafincsquina muthensis Reed. Ordovician and Silurian Fossils from the Central Himalayas. 

 Palseontologia Indica, Series XV, Vol. VII, Mem. No. 2, p. 43, pi. VIII, figs. 13-15. 



This species is represented by a num)>er of specimens, most of them being 

 imperfect. Our best preserved pedicle valve (x 245, PI. II, Fig. 12a) is semicir- 

 cular in outline. The hinge line is slightly shorter than the greatest width which 

 lies about the central part of the shell. The pedicle valve is moderately convex, 

 more or less strongly ai'ched in front. The beak is small and pointed; the hinge 

 area smooth and narrow. The surface is covered by radiating and rather fine 

 plications of unequal strength, which bifurcate and intercalate at various distances 

 from the beak. In the space of three mm. at the front there are about six plica- 

 tions. 



Measurements : 



Greatest width = 19 mm 



Hinge line ^ 18 mm 



Height =13 mm 



Length on curvature — 17 mm 



Pro})ortion of height to width = 1.46 



Shell index - LUG 



