140 CRETACEOUS LAMELLIBRANCHIA. 



1882. Plicatula spinosa, /. Kiesow. Sclirift der Nat. Gesellsch. iu Danzig, 



n. F., vol. V, p. 241. 

 1885. — . iNFLATA, F. Notling. Die Fauna d. baltisch. Cenoman. (Palse- 



ont. Abhandl., vol. ii), p. 15, pi. ii, fig. 3. 

 1887. — — A. Peron. Hist, du Terr, de Craie (Bull. Soc. Sci. 



Hist, et Nat. de I'Yonne, ser. 3, vol. 

 xii), p. 169, pi. ii, fig. 3. 

 1889. — — A. Fritsch. Stud, im Gebiete der bohm. Kreide- 



' format. IV. Die Teplitz. Schicht, 



p. 86, fig. 84. 

 1895. — — E. Tiessen. Zeitschr. der deutscli. geol. Gesellsch., 



vol. xlvii, p. 477. 

 ?1897. — — A. Fritsch. Stud, im Gebiete der biihrn. Kreide- 



forniat. VI. Die Chlomeker Schicht, 

 p. 68, fig. 88. 



Descri])tioii. — Shell oval or somewhat triangular — more distinctly oval in large 

 specimens ; very oblique, margins rounded. Right valve moderately convex, the 

 convexity increasing considerably with age, so that in old specimens the later part 

 of the valve curves considerably from the less convex earlier part. Left valve flat 

 or concave. Right valve ornamented with regular, radial, slightly curved ribs, 

 which are usually few in number, and bear short recumbent spines, which are 

 longer at the anterior and posterior margins ; a few new ribs may be introduced 

 between the older ones. Left valve with similar ribs and spines. 



Measurements : 



(1) (2) (.3) (4) (5) (6) 



Length . 18 22 23 24 25 27 

 Heio-ht^ . 22 23 21 26 28 ' 27 



"O' 



V) 



(S) 



-(9) 



(10) 



(11) 



28 



37 



45 



45 



49 mm 



30 



38 



41 



47 



50 „ 



(2) from the Lower Chalk, Veutnor. 



(8) from the Chalk Marl, Haslingfield. 



(9) from the H. suhglobosus zone. Cherry Hinton. 

 Others from the Totternhoe Stone, Burwell. 



Affinities. — From a comparison of specimens of P. radiola, d'Orbigny, from the 

 Aptian, with specimens of P. inflata, Sowerby, from the English Cenomanian, 

 Pictet, Renevier, and Campiche came to the conclusion thfl,t the two forms could 

 not be regarded as distinct species. My own observations lead me to endorse the 

 opinion of those writers — that examples of the same size are inseparable. Li 

 the Cenomanian, however, the specimens often reach a larger size than any I 

 have seen from the Lower Cretaceous ; in such cases the ventral part of the valve 

 is nearly smooth, or has only indistinct ribs. Figures of a large and also a small 

 form from the Chalk are given by Goldfuss, and good figures of an Aptian speci- 

 men by Pictet and Roux. Peron has named some very small forms from the 

 Cenomanian P. Cotteaui, and considers that P. spinosa, d'Orbigny, is an example 

 ^ Measured obliquely from the umbo to the middle of tlie ventral margin. 



