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XVII. 



ON HOMOTCECHUS {ARCHIE OCID ARTS HARTEANA, BAILY), 

 A NEW GENUS OF PALEOZOIC ECHINOIDS. 

 By PEOFESSOE W. J. SOLLAS, D.Sc, F.E.S. 



[Read June 17, 1891.] 



Literature. — Harte, A. " On a new Eohinoderm (Spatangoid) 

 from tlie Yellow Sandstone of Donegal." Journal Eoyal Geological 

 Society of Ireland, vol. i., p. 67, PL v. 1867. Bailj, W. H. 

 " Remarks on the Palaeozoic Echinidse, Pakechinus, and Archceo- 

 cidaris,'' op. cit., vol. iv., p. 40, PI. iv., 1877. 



Th.e remarkable fossil which forms the subject of the present 

 communication has already been twice brought before the notice 

 of the Royal Greological Society of Ireland ; on the first occasion 

 by its discoverer, Mr. Harte, C.E., who gave a faithful account of 

 its most important characters, accompanied by drawings which, 

 though somewhat diagrammatic, serve sufficiently well for purposes 

 of identification. Whatever deficiencies there might be in Mr. 

 Harte's drawings were subsequently supplied by Mr. Baily's 

 artistic figures, which give a very truthful representation of the 

 general features of the fossil, and as near an approximation to 

 truth in detail as can be expected from the subject, since the fossil 

 is merely a hollow cast of the exterior of the organism preserved 

 in a very fine grained sandstone. Considering this, it is indeed a 

 marvel that so much of detail, down to the number of pores in the 

 genital plates, can still be discerned in it. Mr. Baily greatly 

 added also to our knowledge of the specimen, which he recognized 

 as representing a new species, to which he assigned the name 

 " Sartiana," at the same time provisionally attributing it to the 

 genus " Archceocidaris.'" 



Mr. Harte's description is sufficient, however, to make the 

 species his own, and it certainly, therefore, much rather deserves 

 to be called " Hartii^^ than ^^ Hartiana.'" This, however, in pass- 

 ing ; much more important are certain of the characters of the 



