SoLLAS — A New Genus of PalcBozoic Eckinoids. 153 



fossil itself. These were not overlooked by Baily, but to me they 

 seem to remove the species from Archceocidaris and to render 

 necessary the institution of a new genus for its reception. The 

 chief of these characters are the triserial poriferous zones, the 

 square ridge running down the middle of each ambulacrum, aud 

 the absence of large tubercles, except on some of the adambulacral 

 plates. 



Genus HoMOTCECHUs^ (new). 



Test spherical, regular, apex not depressed. Ambulacra nearly 

 straight, poriferous zones depressed, triserial, interporiferous area 

 an elevated steep-sided ridge bearing two rows of small tubercles 

 or granules, one to each plate, indicated by suture on the summit 

 of the ridge ; to each plate, which is composite, correspond three 

 pairs of pores in the adjacent poriferous zone. Interambulaeral 

 areas about three times as broad as the ambulacral, composed of 

 five rows of plates where broadest, hexagonal, except where 

 adjacent to the ambulacra, then pentagonal : of the pentagonal 

 plates some, but not all, bear a large perforated tubercle. Apical 

 disc regular, five genital plates (basalia), large, mul tip erf orate, 

 four of them with a prominent centrally placed tubercle, the 

 fifth, which is the madreporite, without a tubercle, five ocular 

 plates (radialia) very small. 



A single species, Homotoechus Hartii (Baily). 



Horizon, Calcareous Grit, Lower Carboniferous System. 



Locality, Western Shore of Lough Esk, about six miles from 

 Donegal. 



The large perforate tubercles of the interambulaeral plates, 

 adjacent to the ambulacra, are present on the second and fourth 

 pairs ; the first pair, which abut on the basalia, the third, fifth, 

 and sixth are devoid of tubercles. The series is not clearly 

 preserved beyond the sixth plate. 



Excepting the very small first pairs, the interambulaeral plates 

 are large and approximately equal in size, with a swollen dome- 

 like surface, suggestive of a scrobicula without its tubercle, and 

 giving a characteristic quilted appearance to the test. The plates 

 bear no resemblance to those of Archceocidaris JJrii. 



^ o/xdoTotxvs, well plaited. 



