136 



CYPHOSOMA 



ginal region ; the small pores are arranged in oblique pairs at the sides, and at the upper 

 surface become bigeminal; fig. 10 shows an ambulacral area with its poriferous 

 zones magnified six diameters ; fig. 7 3 exhibits the upper part of the area magnified six 

 times, with the bigeminal arrangement of the pores in the upper part of the zones. 



The inter-ambulacral areas are furnished with two rows of tubercles nearly identical 

 with those of the ambulacral ; they are, however, a little larger than the latter in the upper 

 surface, and are sm-rounded by areolae that are placed wider apart. The secondary 

 tubercles are very small and unequal in size; they form a series near the zones, one mam- 

 millated tubercle rising in each plate from the midst of numerous granules. They are 

 most apparent at the lower surface and the ambitus, and are rare on the upper surface. 



The miliary zone is wide, naked, and depressed in the upper surface, forming at the 

 ambitus and lower surface a zigzag line, which defines the contour of the plates. The 

 granules are large, and those surrounding the primary tubercles at the ambitus send pro- 

 longations into the areolae, which impart a radiated character to the structure of these 

 parts. The intermediate granules are more or less abundant, and form circles or semi- 

 circles around the areolae. The small mouth-opening is lodged in a concave depression 

 in the base. The peristome is circular, and divided by feeble incisions, the lobes of 

 which are nearly equal. The apical disc is absent. The opening is large, pentagonal, 

 and angular, and in our large specimen is about five lines in diameter. 



The spines are long, slender, and spatulate, one fourth longer tiian the diameter of the 

 test, to which they are sometimes found adherent and in situ. 



Affinities and Differences. — C. coroUare is readily recognised by its moderate size, 

 depressed circular test, sometimes subpentagonal ; the pores are unigeminal on the sides 

 and bigeminal on the upper surface, with small secondary tubercles at the base near to the 

 zones ; the miliary zone is nude and depressed near the summit ; the mouth-opening is small, 

 and lodged in a concave depression. By these characters it may be distinguished from 

 C. tiara and young examples of C. granulosim, both of which it resembles much. 



LocaUiy and Stratigrapldcal Position. — This Urchin is very common in the upper 

 flinty Chalk of Brighton, Gravesend, and Woolwich. In France M. Cotteau enumerates 

 the following localities in which it is rarely found in the Etage Senonien : — Senneville, 

 Saint-Pierre en Port (Craie supericure, M. Hebert) ; Seine Inferieure, La Herelle (Oise) ; 

 Pinterville (Eure) ; Villeneuve-sur-Yonne (Yonne) ; Meudon (Seine-et-Oise) ; Sarlat 

 (Dordogne) ; Tercis (Landes). 



History. — The history of this species, one of the oldest Cyphosomas, is very difficult 

 to trace, as our table of synonyms has already exposed. Lister and Klein have both 

 figured it, and Parkinson has given a very good figure of it under the name of Echinites 

 saxaiilis in his 'Organic Remains.' Klein's name, however, has the priority, and 

 therefore is retained. 



