PECTEN. 209 



1878. Neithea ^equicostata, E. Bayle. Explic. de la Carte geol. de Prance, 



vol. iv, pt. 1 (Alias), pi. cxxii, fig. 4. 

 1882. Janira jequicostata, /'. de Loriol. Gault de Cosne (Mem. Soc. Pal., 



Suisse, vol. ix), p. 102, pi. xiii, 

 figs. (J— 8. 

 1885. — — F. Notling. Die Fauna d. baltisch. Cenoman. 



(Palaeont. Abhandl., vol. ii), p. 21. 



1893. — (Vola) jequicostata, B. Michael. Zeitschr. d. deutsch. geol. 



Gesellsch., vol. xlv, p. 237. 



1894. Vola ^qtjicostata, A. HennUj. Om Ahussaudst. (Geol. Foren. i Stockholm 



Forhandl., vol. xvi), p. 520. 



1895. Janira jequicostata, E. Tie&sen. Zeitschr. d. deutsch. geol. Gesellsch., 



vol. xlviii, p. 472. 

 1901-2. Vola .equicostata, P. Choffat. Faune Cret. Portugal, vol. i, ser. 4, p. 152, 



pi. iii, fig. 10. 



? Non 1847. Pecten ^equicostatus, J. Muller. Petref. Aachen. Kreideformat., pt. 1, 



p. 33. 

 Non 1850. J. de C. Sowerby. In F. Dixon's Geol. Sussex, 



p. 350, pi. xxviii, figs. 17, 18 

 (=8exco8tatus). 



Description. — Shell ovate, equilateral; ventral margin very convex and rounded; 

 antero- and postero-dorsal margins slightly concave. 



Right valve very convex, with a prominent incurved umbo, and with from 

 thirty-four to fourty-four rather small, rounded ribs of nearly equal size, except 

 those near the anterior and posterior margins, which are smaller. The ribs are 

 separated by rounded furrows of about the same width as the ribs. Both ribs and 

 furrows are smooth, or nearly smooth. Near the antero- and postero-dorsal 

 margins are narrow, smooth areas without ribs, the anterior area being slightly 

 smaller than the posterior. Ears of moderate size, triangular, nearly equal, smooth, 

 or with tine concentric ridges. 



Left valve flat or slightly concave, with ribs similar to those of the fight valve. 



Measurements : 



(1) (2) (3) 



Length . 14 . 10-5 . 9 mm. 



Height . l(') . 12 . 11 „ 



(1, 3) Upper Greensand (zone of Pecten asper), Haldon. 

 (2) ,, „ „ ,, ,, Worbarrow. 



Affinities. — This species is distinguished from P. (Neithea) quinquecostatus by 

 the ribs being of equal size, and smooth or nearly smooth; also by the ventral 

 margin of the shell being evenly rounded and by the areas being without ribs. 

 D'Orbigny's figure shows six more prominent ribs, but I have seen faint indications 



