154 Scientific Proceedings, Royal Dublin Society. 



The affinities of Homotcechus are naturally witK the Palse- 

 echinoidea, the multiperf orate character of the basals, and the 

 presence of more than two rows of plates in the interamhulacra 

 involve so much ; but were these features not present we should, 

 on the evidence before us, prefer to refer the genus to the 

 Glyphostomata rather than to the Cidaridse. The ambulacra, 

 though in some respects peculiar, forcibly remind us of the 

 Grlyphostomata. It is not simply that they are broader than in the 

 Cidaridse and with more numerous rows of pores — in the Melonitidse 

 we find these characters — nor that they are depressed on each side 

 of a tuberculated ridge, somewhat similar to that of, say, Gonio- 

 pygiis, but the resemblance lies rather in the closeness of the pore 

 triplets to one another, and their union into a composite ambu- 

 lacral plate, reminding us of the composite ambulacral plates of 

 such a form as Stomechinus, and offering very little resemblance 

 to those of any Palaeozoic Echinoid, or of any Cidarid, not 

 excluding Tetracidaris. 



There is no evidence of imbrication of the plates of the corona, 

 of which, however, only the apical half is preserved ; in this there 

 is every indication that the plates abutted against one another. 



Amongst the Palse-echinoidea the place of Homotcechus is with 

 the order Perischoechinoidea of M'Coy, but from the information 

 at present in our possession it is not possible to certainly place it 

 in any of the recognized families of the order. 



My friend, Mr. Sladen, to whose authority I willingly defer, 

 informs me that in his opinion its affinities are closest with the 

 Melonitidse, to which family he would, at least provisionally, 

 relegate it. 



