FROM THE CORNBRASH. 123 



PSEUDODIADEMA VAGANS, Phillips. 



Cidakis vagans. Phillips, Geology of Yorkshire, pi. 7, fig. 1, 1829. 



Diadema vagans. Desmoulins, Etudes sur les Echinides, p. 316, 1835. 



— — Morris, Catalogue of British Fossils, 1843, p. 51. 



Morris, Catalogue of British Fossils, 2d edit., 1855, p. 72. 



— Woodward, Memoirs of the Geological Survey, Decade V, Notes 



on Fossil Diademas. 

 Pseudodiadema vagans. Desor, Synopsis des Echinides Fossiles, p. 65. 



The type specimen of this species, with many other valuable fossils, was lost in 1835 ; 

 there is, therefore, now some difficulty in making out the true form figured as Cidaris 

 vagans'm the ' Geology of Yorkshire.' Professor Phillips has, however, most kindly com- 

 municated, ex memorid, all the facts he recollects relating to this species, and has sent to me 

 for comparison a Diadem which he collected at Whitwell, Yorkshire, from the Bath Oolite. 

 In speaking of this urchin my friend observes — "It seems, except that it is larger, to revive 

 my recollection of Cidaris vagans." 



Having carefully compared this specimen with Pseudodiadema depressum, which it 

 most nearly resembles, 1 find it agrees so well with that urchin in all its details which 

 admit of comparison, that I believe it is referable to the same species; the under part 

 of the test being imperfect, the base and mouth opening cannot be made out. The 

 examination of the upper surface, and the poriferous zones, which are well preserved, 

 has convinced me, that if it is regarded as a genuine example of Philips's species, Cidaris 

 vagans must be considered a synonym of Pseudodiadema depressum, Agassiz. My 

 friend, Mr. John Leckenby of Scarborough, has kindly communicated two Diadems from 

 the Great Oolite of the Nab rock ; these urchins are nearly indentical with Prof. Phillip's 

 Whitwell specimen ; the pores in the upper part of the zones, in the Nab rock specimens, 

 however, manifest a disposition to become slightly bigeminal, an irregularity which I have 

 often seen in true unigeminal forms, and regard only as an occasional variety of the 

 species. In all probability these urchins may represent C. vagans, as most of the Great 

 Oolite Echiniderms are likewise found in the Cornbrash. 



