OP THE rURBECK FORMATION. 339 



In specimen XbJ Mus. Pract. Geol., the central swelling is well 

 marked, without any posterior thickening of the valve. 



3. Cypridea Dunkeri, sp. nov. (PL YIII. figs. 9, 10, and 17.) 



Cypridea granulosa, Eomer (non Sowerby), Yerst. nordd. Ool.- 

 Geb. 1839, p. b2, pi. 20. fig. 24. 



Cyjpris granulosa^ Dunker (non Sowerby), Monogr. nordd. 

 Wealdenbild. 1846, p. 60, pi. 13. figs. 31 a, h. 



Cypiis granulosa^ Porbes (non Sowerby), MS. July 18, 1851. 



Cypris grcmulata, Porbes, MS. July 23, 1854. 



Ct/pris granulata, Porbes, in LyeU's Elem. Man. Geol. 5th edit. 

 1855, p. 295, fig. 337 c; Elem. Geol. 6th edit. 1865, p. 378, 

 fig. 371 c. 



Cypridea granidosa, H. Woodward (non Sow.), Cat. Brit. Foss, 

 Crust. 1877, p. 88. 



Length | mm. 



This has the obovate form and general features of C. punctata, 

 but it possesses granules or small tubercles scattered irregularly 

 over the surface. This is shown in Porbes's letter of July 18, 1851, 

 but too roughly. In our figured specimens the tubercles vary in 

 size, being feeble in the neat, small, nearly symmetrical figs. 9, 10, 

 and strong in the larger and coarser fig. 17. In one individual 

 (fig. 10) the punctation consists of small and rather oblong pits on 

 the anterior third of the valve, with an obscurely radiate arrange- 

 ment. Taking both Purbeck and Wealden specimens of this species 

 in view together, we find much variation in convexity and in 

 tubercles ; occasionally some of these are sharp (near Brook Point). 



This subovate, or rather obovate, form has been confused vnth 

 the suboblong Cypridea granidosa (Sow.). The latter is distin- 

 guished by its larger size, more oblong shape, and the tendency of 

 its granules to leave the middle of the valve bare. This is plentiful 

 in the Middle Purbeck, whilst the obovate form, with granules 

 distributed over the whole surface, is rare in the Purbecks * ; and 

 this agrees with E. Porbes's note to Mr. Bristow (see above, p. 314). 



In consequence of the confusion of names, I now dedicate this 

 species to the memory of my late friend Dr. W. Dunker, of Marburg, 

 by whom it was figured and described much more clearly and 

 perfectly than by his predecessor P. A. Romer. 



Cypridea DunJceri is rare in the Upper and Middle Purbeck, but 

 of rather more frequent occurrence (though rarely common) in the 

 Wealden beds. It is met with in the Upper Purbeck at Mewps 

 Bay (specimen Xb|-, M.P.G.), and at Durlston Bay, specimen 

 no. 40. In the Middle Purbeck it occurs at Ridgway (Xb-4-, 

 M.P.G.); also in a specimen, given to me by the Rev. O.Pisher, and 

 probably from Mewps Bay, there associated with Gytlieridea punc- 

 tata, var. posticalis, Metacypris Forhesii, and Darivimda leguminella. 



The synonyms indicate that it also belongs to the black Cypri- 

 diferous shales of North Germany (see also above, p. 319). 



* Except at Swindon, see p. 330. 



