536 H. L. Haivkins — The Species of Cidaris 



shape is that of a very acute isosceles triangle. At the abruptly 

 truncated base is a shallow acetabulum. The convex (outer) side 

 of the radiole is covered with fine, slightly granular lines (about 

 seven in average specimens). The flat (inner) surface is quite smooth. 



Comparison with other species. — The outstanding features of the 

 test of C. faringdvnetisis are its great size, the coarse crenelation of 

 the primary tubercles, the large size, but slight prominence, of the 

 scrobicular tubercles, and the paucity and coarseness of the miliary 

 granules. The characteristic features of the radioles are their length, 

 the great development of their collerettes (and their separation from 

 the stem by a bourrelet), and the faint corollge at the distal ends. 

 The distinction between this and the associated species will be dealt 

 with after the description of that form. Apart from the species already 

 discussed, there remains only one type with which comparison may 

 be useful. The simple anibulacral granulation serves to distinguish 

 C faringdonensis from most Neocomian and Cenomanian species. 



G. vesiculosa, Goldf., with which Wright compared the species, 

 has notably broad miliary zones. Except in var. maxima, the 

 miliaries occupy a very small part of the interambulacral plates of 

 C. faring donemis. The scrobicules in the latter species are shallow, 

 in the former they are deep. 



In the case of the radioles the peculiarities of C. faringdonensis 

 mark it off sharply from other forms, except from a radiole described 

 by de Loriol in 1863 as C. salevensis, " Desor in notis," 1862. This 

 seems almost identical with the Faringdon radioles, but, since only 

 a broken radiole of C. salevensis \?>'kno\\Ti, I have thought it inadvisable 

 to certainly identify it with C. faringdonensis, especially as it would 

 necessitate a change in the nomenclature. The recognition of species 

 of Cidaris founded on the radioles alone is quite impracticable, and 

 merely complicates the already overburdened synonymy of many 

 species whose structure is well known. 



Horizon and Localities. — Aptian (T^ower Greensand) of Faringdon, 

 Berks ; also from TJpware, Cambs {fide Keeping), and perhaps from 

 the Ardennes {fide Barrois). 



(PLATE XXVI.) 

 5. Desckh'Tion of thk Shx'ond Species of Faringdon Civaris, 



ClVAIilS COXWELLENSIS, Sp. UOV. 



(The ' Sponge-gravel ' pits are near the village of Great Coxwell.) 



Synonymy 



1909. Cidaris pretiosa, Treacher [nan Desor), Proc. Geol. Assoc, vol. xxi, 

 p. 119. 



Diagnosis: Test, var. typica, nov. — Form of medium size, fairly 

 high, almost equally flattened adorally and adapically. Ambulacra 

 about one-sixth the width of the interambuhicra, with four rows 

 of perradiad granules, the outer rows being the larger. Inter- 

 ambulacral plates thick, with obscure pits at the interradial angles 

 and on the transverse sutures ; scrobicules circular, bosses smooth, 

 mamelons large, covering nearly all the platform, finely perforated. 

 Scrobicular circle of very small, well-spaced secondary tubercles 



