58 CIDARIS 



Cidaris subvesiculosa, Coquand. Bull. Soc. Ge'ol. de France, 2e serie, torn, xvi, p. 



1013, 1860. 



— — • Cotteau et Triger. £chin. du dep. de la Sarthe, p. 250, pi. 



xli, figs. 1—9, 1860. 



— — Cotteau. Paleontologie Francaise, Ter. Cretace, tome vi, p. 



257, Pis. 1059—1061, 1863. 



Test large, circular, inflated, nearly equally depressed at both poles ; ambulacral areas 

 slightly flexed, wide, with six rows of nearly equal-sized granules at the equator, 

 diminishing to four and two rows at the poles, the external series being the largest and 

 most persistent ; poriferous zones narrow, depressed, and composed of simple oval pores, 

 separated from each other by an elevation of the septum ; inter-ambulacral areas wide, six 

 or seven large plates in a column ; the three equatorial plates with large areolae, those 

 near the peristome small, and the two upper plates near the disc with small rudi- 

 mentary tubercles; areola? circular, depressed, surrounded by a ring of mammallated 

 granules, boss flat, with a smooth summit, tubercle moderate and perforated ; miliary zone 

 wide, filled with fine close-set homogeneous granules, disposed in very regular horizontal 

 lines, radiating from the scrobicular circle to the border of the plates ; peristome small 

 and pentagonal ; apical disc large, ovarial plates wide, narrow, and perforated at a 

 distance from the border ; ocular plates heart-shaped, with marginal orbits. Two con- 

 secutive series of cuboidal anal plates arranged within the pentagonal area formed by the 

 ovarials ; vent small and sub-central. 



Spines slender, elongated, and cylindrical ; surface covered with longitudinal elevations, 

 having a fine serrated or spinous border gradually becoming attenuated towards the base ; 

 neck short, with longitudinal lines ; milled ring prominent, articular surface without 

 crenulations. 



Dimensions. — Specimen fig. 5 — height, one inch and one tenth; transverse diameter, 

 one inch and seven tenths. 



Description. — This urchin has been mistaken for Cidaris vesiculosa, Goldf., from 

 which it differs, however, in many important characters ; these have already been indicated 

 in the description of that species (p. 41). The test is in general of moderate size, and 

 nearly equally depressed at both poles ; the ambulacral areas are slightly flexed, with six 

 rows of granules at the equator ; the external rows have larger mammillated granules than 

 the inner rows, which gradually disappear as the area becomes narrower near the peristome 

 and disc ; the poriferous zones are narrow, depressed, and sub-flexuous ; the por«s are 

 oval, and oblique as they approach the disc, and the septa have small elevated granules 

 between the holes. The inter-ambulacral areas are large, the plates wide and deep, six or 

 seven in a column (PL VIII, figs. 4, 5), the areolas are circular and moderately depressed ; 

 they are widely spaced out at the upper surface, and placed closer together at the infra- 



