530 H. L. Hcuckinn — The Species of Cidaris 



Having accumulated, largely owing to the constant help and 

 encouragement of my friend Mr. LI. Treacher, many hundreds of 

 specimens of Cidaris-revanins fiom Fariiigdon, I have heen able to 

 make an exhaustive comparative study of both types. There seem to 

 be not more than two species of Cidaris represented among the very 

 numerous fragments that I have seen, each species showing two 

 fairly parallel varieties. (No account is taken in the present paper 

 of the not infrequent waterworn radioles of Paracidaria florir/enima, 

 which have obviously been derived from the Corallian of the 

 neighbourhood.) 



I have examined Wright's type- specimens of C. faringdonensis, 

 which are in the Museum of Practical Geolog}' at Jerrayn Street, and 

 can confidently state that both the plates figured in the monograph 

 (1864) belong to the same species. This is a contrary conclusion to 

 that reached by Lambert (1892), but certainly, from a study of the 

 figures alone, their reference to distinct species was justifiable. 



Unfortunately the Cidarids of the 'Sponge-gravels' are almost 

 always found in a disarticulated condition, and in no cases have the 

 primary radioles and their tests been discovered in even probable 

 association. jSow the features of the radioles were well described 

 and figured by Wright, while the treatment of the plates of the test 

 was short and inconclusive. Judging by this fact alone, it would seem 

 expedient to regard the species C. faring doiunsis as having been 

 founded on the radioles, in case it should be determined that the 

 plates and radioles figured under that name belong to different species. 

 Fortunately, in this case, there seems no doubt but that the plates 

 of the type he figures on pi. ii, figs. 6 and 7 of the monograph, do in 

 reality belong to the same species as the radioles of fig. 8. I have 

 counted the actual numbers (of recognizable specimens) of plates and 

 radioles of over a thousand specimens of both the types present at 

 Faringdon, and find that the series corresponding with Wright's 

 figures are almost twice as numerous as those of the second species. 

 Adding to this the con.sideration that the average size of plates and 

 radioles of tlie already figured types is much greater than that of the 

 other forms, it seems to be a safe assertion that C. faringdonenais^ 

 AVright, is a valid species, of which both the test and radioles are 

 known. 



Of the other type, not without great hesitation, I have made a new 

 species, the characters of which, as will be found in the description, 

 are much more satisfactorily known than are those of C faringdonensis. 



3. Species that have been ascribed to C. faringdonensis. 



In 1873 de Loriol, in the Echinologie Hehetique, p. 51, pi. iii, 

 figs. 31-5, announced tlie discovery of C. faringdonensis for the first 

 time out of England. Judging from liis remarks, he seems to have 

 referred only to Wright's description and figures in making the 

 specific determination. The specimens he described are a broken 

 test and some very fragmentary radioles. The latter certainly bear 

 a considerable resemblance to the radioles of Wright's figures, although, 

 as de Loriol himself observed, their collerettes are comparatively 



