60 CIDARIS 



species were compared with each other, they would be found to be only so many cognate 

 varieties of one forui. 



Locality and Stratigraphical position. — Tliis species is found in the Upper Chalk of 

 Kent, Sussex, and Wilts. 



In France M. Cotteau gives the following localities in which it is very common in the 

 Etages Turonien et Senonien : Bolbec (Seine-Inferieure) ; Houguemarre, Vernonnet, Petit- 

 Andelys (Eure) ; Notre-Dame-du-Thil, Tartigny (Oise) ; la Ealoise (Somme) ; Saint- 

 Eraimbault, IMar^on, les Menus (Sarthe) ; Yilledieu, Villiers (Loir-et-Cher) ; Semblancay, 

 Limeray (Indre-et-Loire) ; Briolay (Maine-et-Loire) ; Barbezieux, Aubeterre, Lavalette, 

 Salles (Charente) ; Royan, Saint-Georges Talmont, Saintes, Cognac (Charente-Inferieure) ; 

 Perigueux, Tretissac, Neuvic (Dordogne) ; Bugarach, Soulatge (Aude). 



History. — This urchin was first figiu-ed by Parkinson in 1811. The test and spines are 

 sufficiently well drawn, in the absence of a description, to enable us to identify the species. 

 In 1822 Mantell described, under the name C. cretosa, a Cidaris represented by Parkin- 

 son ('Organic Remains,' Vol. Ill, PL I, fig. 11), and united to fig. 3, PI. IV, of the 

 same work, which served as the type of C. snhvesicidosa. Professor Eorbes identified this 

 species with the C. vesiculosa, Goldf., and figured it under that name in Dixon's ' Geology 

 of Sussex.' In 1850 M. d'Orbigny, in his 'Prodrome de Paluontologie,' separated it from 

 that form under the name subvesiculosa, which has been adopted by MM. Desor, Cotteau, 

 and other authors. 



Cidaris Merceyi, Cotteau. PI. VIII, figs. 1, 2, 3. 



Cidaris Merceyi, Cotteau. Paleont. Fran9aise, Ter. Cretace Ecbinoderraes, toin. vii, 

 p. 281, pi. 1068, 1862. 



Test large, circular, and elevated above, inflated and depressed below; ambulacra 

 narrow, depressed, and slightly flexed ; two rows of small regular mammillated granules 

 on the external border, and four rows of smaller, irregular granules on the central portion 

 of the area ; poriferous zones narrow, flexed, composed of round pores in oblique pau's ; 

 inter-ambulacra wide, six or seven large plates in a column ; tubercles well developed at 

 the base and equator, but small and obsolete on the upper surface ; areolae circular, 

 depressed, margin surmounted by a circle of regular mammillated granules. 



Dimensions. — Height, two inches ; transverse diameter, two and a half inches. 



Description. — This remarkable urchin, which appears to be an elevated variety of 

 Cidaris subvesiculosa, has been described by j\I. Cotteau as a distinct species under the 



