THRACIA. 241 



margin nearly straight, Avitli a considerable ventral slojie ; anterior margin rounded, 

 passing gradually into the convex ventral margin ; posterior margin rather short, 

 oblique, more or less truncated, forming a rounded angle with the nearly straight 

 and veutrally sloping postero-dorsal margin. Umbones rather prominent, curved 

 inwards and slightl_v backwards. Postero-dorsal part of valves cduipresseil, some- 

 times with a small cariiui. Surface with numerous small concentric growth-ridges. 

 Measiir<'inenfti .■ 



(1) (2) (3) 



Length . 68 . 64 . VJ mm. 



Height . 52 . 4(i . :38 „ 



Thickness . 30 . 28 . 22 „ 



(1—3) Speetou. 

 Affinities. — It is probable, as maintained by Harbort,' that Thracia striata, 

 Weerth,- is not specifically distinct from 7'. I'liillipsi. 



Bemarls. — The greater part of the shell has disappeared from most of the 

 examples found at Speetou, and usuall}- some part of the margin of the cast has 

 also been lost. I have not seen sufficient examples to enable me to determine 

 whether the variation of this species in England is as great as in the case of the 

 specimens found in Schaumburg-Lippe and described by Harbort. 

 Ti/jte. — From Speetou, in the York Museum. 

 Distribution. — Speetou Clay (zone of Belemnites Jacitlnm) of Speeton. 



Tiii;\ciA ROTUNDATA (So^vrA//), 18:56. Plate XXXIX, fig. M).i,b. 



1836. Panop^a ROTUNDATA, /. de C. Soirerhij. Traus. Geol. Soc, ser. 2, vol. iv, 



■ pp. 129, 337, pi. xiu, fig. 2. 

 1850. Lyonsia sdbbotundata, A. trOrbUjnij. Prodr. de Pal., vol. ii, p. 74. 

 1854. Myacites eotundata, /. Morris. Cat. Brit. Foss., ed. 2. p. 214. 

 1865. Thracia subrotundata, F. J. Pirtct and G. Cnnqiiche. Foss. Terr. Cret. 



Ste. Ci-oix (Mat'.'r. Pal. Suisse, ser. 4), p. 120. 

 1870. CoRiMYA ROTUNDATA, F. Sloliczlca. Palscout. Iiulioa, Cret. Faima S. ludia, 



vol. iii, p. 72. 



Description. — Shell regularly convex, oval, slightly iuc'(|uivalv(' and iniMpiilateval. 

 Anterior an<l ventral margins convex, forming a regular curve. Dorsal part of 

 posterior margin ol)lique, forming an angle with the ventral part. Umbones broad, 

 in contact, with a narrow, sharp, curved carina extending to tlie posterior angle 

 and limiting a triangular, concave, postero-dorsal area, which is ornamented with 

 fine ribs running parallel to the posterior margin. Sides of valves with similar 

 ribs extending in a radial direction. 



^ 'Die Fauna d. Schauiiiburj.c-Lippe'sclieu Kreideuiulde ' (1905), p. 78. 



= 'Neocomsundst. im Teutolmrg. Waldo" ('Pala-ont. Aliliaiidl. ' II, 1884), p. 40, pi. viii. fii,'. 10. 

 Wollemaun, ' Die Bivalv. u. Gastrop. d. deutsoli. n. liolliiud. NeoL-oins ' (1900), p. 1 40, pi. vii, fig. 1. 



32 



