from the Loirer Greensand. 539 



show that the striations on the outer surface become specially 

 prominent towards the distal end. 



Comparison loith other apecies. — The outstanding features of the 

 test of C. coxwellensis are the smoothness of the platforms and great 

 size of the mamelons of the primarj^ tubercles ; the minute size of 

 the scrobicular tubercles; and the paucity of the granulation (except 

 in var. major, where the miliaries az'e liorizontally arranged). The 

 main characteristics of the radioles are the coarseness of their granu- 

 lation, the inflation of one side of the stem, and the shortness and 

 undefined limits of the coUerette. 



A comparison of the above summary of the characters of C. cox- 

 wellensis with that given for C. faringdonensis will be sufficient to 

 show the extreme contrast existing between the two Faringdon 

 species. Even a fragment of a plate or a section of a radiole are 

 sufficient to distinguisli to which foj-m they belong. 



The slight development of miliaries on the interanibulacra of 

 C. coxivellensis tyjjica, and their linear arrangement in var. major, are 

 characters which separate the species from practically all JSeocomian 

 and Cenomanian types. When the large development of the mamelon 

 and the feebleness of the scrobicular tubercles are taken into account, 

 a still more thorough distinction is seen. Perhaps it is ■with 

 C. pretiosa, Desor, that tlie new species has most affinity. A com- 

 parison with that species is natural, owing to the extreme similarity 

 of the radioles in both forms. However, in C. pretiona a very 

 anomalous feature in the ambulacra — that of a small outer, and large 

 inner, row of granules in the interporiferous area — is a sufficient 

 contrast from the definitely inverse proportions of the similarly 

 placed granules in C. coxwellensis. 



The radioles are very like those of C. pretiosa, differing from them 

 only in the more marked corolla developed at the distal end. In 

 view of the great abundance of radioles of C. coxioellensis, and the 

 complete absence of any test fragments referable to C. pretioaa, it 

 seems clear that this similarity of the radioles is no criterion of specific 

 identity. In fact, since the radioles found on one specimen of 

 a Cidaris may vary from one another very profoundly, it is natural 

 that the converse condition of similar radioles in different species 

 should occur. 



Horizon and Locality. — Aptian (Lower Greensand) of Faringdon, 

 Eerks. 



6, Undetermined Fkagments. 

 Considerable numbers of jaw-fragments, chiefl.y hemipyramids and 

 teeth, occur in association with the other Cidaris remains in the 

 ' Sponge -gravels'. They are usually waterworn, but the measure- 

 ments of the pyramids, and their large size, indicate that they belong 

 to Cidaris. The smaller fragments probablj'' belong to Pseudodiadema 

 and Peltastes. 



In conclusion, I wish to express my gratitude to Mr. LI. Treacher 

 for placing his unrivalled collection of Faringdon Echinoids at 

 my disposal for the purpose of the foregoing description ; and to 



