PINNA. 97 



? 1888. Pinna Eobinaldina, P. Choffat, Stratigr. et Paleont. d'Angola (Mem. Soc. 



phys. et d'hist. nat, <!<• Geneve, vol. xxx, 

 No. 2), p. 86, pi. v, figs. 4, 5. 



? 1903. C. Bnrclchardt. Jura u. Kreidef. d. Cordillere (Palce- 



ontographica, vol. 1), p. 79, pi. xv, 

 figs. 6, 7. 



? 1905. — cf. Eobinaldina, E. Harbort. Fauna d. Schaumburg-Lippe'schen 



Kreidemulde (Abhandl. d. k. preus- 

 sisch. gcol. Laudesanst., N.F., Heft 

 45), p. 47, pi. v, fig. 5 ; pi. vii, 

 figs. 2, 3. 



Description. — Shell straight, much elongated; pyramidal, slightly compressed; 

 margins nearly straight; section sub-quadrangular. 



Each valve is divided into two parts, which meet at an angle. The dorsal part 

 is smaller and more flattened than the ventral part, and is ornamented with from 

 G to 8 or more ribs, which are narrow, strong, and nearly equi-distant. The ribs 

 are separated by broad, shalloAV, rounded depressions ; both depressions and ribs 

 are crossed by very fine, somewhat irregular, concentric ridges, which sometimes 

 give a slightly serrated appearance to the ribs. The ventral part of each valve is 

 moderately convex, and its dorsal portion is ornamented with from 5 to 7 radial 

 ribs similar to those on the dorsal part of the valve, but decreasing in size ventrally; 

 the last one or tAvo of these ribs sometimes become irregular and discontinuous. 

 These radial ribs and their interspaces are crossed by fine concentric ridges. The 

 ventral portion of the ventral part of the valve is ornamented with strong growth- 

 ridges or folds, which curve rapidly in the direction of the umbo, and form an 

 acute angle where they meet the ribs. 



Measurements : 



(i) (2) 



Length . 135 . 94 mm. 



Height 49 . 41 „ 



(1) Perna-hod, Atherfield. 



(2) Crioceras-bed, Whale Chine. 



Affinities. — The figure of P. gracilis, Phillips, 1 is not sufficiently good to enable 

 one to form a satisfactory idea of the character of the species, and the type cannot 

 now be found. But other specimens from Speeton, although very imperfectly 

 preserved, are sufficient to suggest that P. gracilis is probably identical with /'. 

 Eobinaldina. 



It is suggested by Pictet and Campiche that P. tetragona, Sowerby, 2 from the 



1 ' Geol. Yorks.' (1829), p. 122, pi. ii, fig. 22. 



2 <Min. Conch.,' vol. iv (1821), p. 9, pi. cccxiii, fig. 1; Morris, 'Cat, Brit. Foss.,' ed. 2 (1854), 

 p. 180; P. subtetragona, d'Orbigny, ' Prodr. de Pal.,' vol. ii (1850), p. 105; Pictel and Campiche, 

 ' Terr. Cret. Ste. Croix' (1867), p. 537; non P. tetragona, Brocchi, 1814. 



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