200 CRETACEOUS LAMELLIBRANCH1A. 



Pecten (Neithea) cometa (d'Orbigny), 18-17. Plato XXXIX, figs. G— 10. 



1847. Janika cometa, A. d'Orbigny. Pal. Franc. Terr. Oct., vol. iii, p. 040, 



pi. ccccxlv, figs. 15 — 20. 

 1850. — — Prodr. de Pal., vol. ii, p. 170. 



1868. — — A. Briart and F. L. Comet. Descript. Mineralog. Greol. 



et Pal. de la Meule de Bracquegnies 



(Mum. cour. et Mem. des Sav. 



{Strangers, vol. xxxiv), p. 50, pi. iv. 



figs. 23, 24. 

 1870. — F. J. Pictet and G. Camjnche. Foss. Terr. Oct. Ste. Croix 



(Mater. Pal. Suisse, ser. 5), p. 252. 



Description. — Shell small, subtriangular, much higher than long, nearly equi- 

 lateral. Antero- and postero-dorsal margins long; ventral margin very convex, 

 with deep incisions between the main ribs. Ears very unequal ; the anterior very 

 long, the posterior small. 



Right valve very convex, with a greatly incurved umbo, and five l very 

 prominent angular ribs, which are crossed by numerous fine concentric ridges. 

 The main ribs are separated by broad, deep, rounded depressions in which from 

 three to seven slightly raised radial ribs occur ; these small ribs are flattened and 

 separated by narrow grooves, and bear numerous fine ridges placed transversely. 

 At distant intervals from two to four strong growth-ridges may occur. 



Left valve flattened, with five strong, rounded radial ribs separated by broad 

 interspaces, both being crossed by fine concentric ridges. A few strong growth- 

 ridges may occur. 



Measurements : 





(1) (2) (3) 





(4) 



(5) 



ength 



. U . 13-5 . 11 





10 



11 mm, 



eight 



. 18 . 19 . 14-5 



(1, 2) Cenoinauian, Wilmington. 

 (3, 4) Upper Greensand, Warmins 



ter. 



13 



. io „ 



Affinities. — This species is closely allied to Janira longicauda, d'Orbigny, 2 but is 

 distinguished from it by the main ribs being narrower and more angular. It is 

 also nearly related to V. notabilis, Groldfuss, 3 but differs in possessing five main 

 ribs instead of six, and apparently also in being relatively higher. 



1 Occasionally a sixth rib, not quite so prominent as the others, occurs near the anterior margin. 



2 'Pal. Franc. Terr. Oct.,' vol. iii (1847), p. 639, pi. ccccxlv, figs. 9—14. Geinitz, "Das 

 Elbthalgeb. in Sachsen" (' Palseontographica,' vol. xx, pt. 1, 1872), p. 202, pi. xlv, tigs. 1(5, 17. 



3 'Petrel'. Germ.,' vol. ii (1833), j>. 56, pi. xciii, fig. 3. Geinitz, "Das Elbthalgeb. in Sachsen" 

 i Palaeontographica,' vol. xx, pt. 1, L872), p. 202, pi. xlv, tigs. 10—12. 



