98 PEOF. p. M. DTJKCAN S EEYISION OF THE 



perforate, crenulate, primary tubercles, largest actinally; boss 

 spreading, mamelor) globose and prominent, placed upon the 

 aboral third of a plate ; miliaries abundant, those nearest the 

 tubercle elongate, and radiating more or less towards other 

 miliaries which encircle them, arrangement confused further 

 away. Plates high, compound, usually three pairs of pores and 

 rarely four to a compound plate, almost in straight series or 

 slightly in arcs ; component plates are low, broad primaries with 

 straight transverse sutures. On the tumid actinal surface a few 

 large tubercles exist and sometimes alternate ; they have distinctly 

 radiating, long miliaries, resembling short costse, between the boss 

 and the usual circle of miliaries. 



Interradia broad, with two vertical rows of primary tubercles, 

 resembling, but slightly larger than, the ambulacral ; a few secon- 

 dary tubercles may exist ; miliary tubercles numerous, irregularly 

 placed near the edges of the plates, in circles around the bosses 

 and united to them by more or less elongated ridges ; a costa- 

 like projection, or several, placed adorally to the primary tubercles, 

 arising from them or from the adoral edge of a circle of sur- 

 rounding miliaries, and thence extending to, or over, the adoral 

 coronal suture of the plate. Tubercles and their surrounding 

 radiations and circle of miliaries largest and most distinct actinally. 



Ambulacral and interradial transverse sutures grooved, espe- 

 cially actinally to the tubercles, and the median sutures also. 



Peristome small, sunken, with very slight branchial incisions. 



Fossil. Cretaceous : England, Europe, and N. Africa. Middle 

 Eocene : Europe. Upper Tertiary ? : Europe. 



A comparison of the drawings of Glyplwcyphus radiatus, Honing, 

 sp., in the works of Desor, Cotteau, and Wright will satisfy most 

 students that either the variation of characters must be con- 

 siderable or the details of structure have been drawn from 

 indifferent specimens. Having had the advantage of examining 

 perfect specimens, some of which are in the National Collection, 

 it appears that the amount of variation is not great. It amounts 

 to a stouter condition of the invariably narrow apical ring 

 around the large periproct, especially of the anterior plates, the 

 presence of an extra pair of pores in some ambulacral plates, a 

 larger development of the ambulacral tubercles actinally, and 

 the presence or absence of one or more short costa-like projec- 

 tions, placed adorally to eacli interradial tubercle. The grooving 

 of the transverse sutures of the interradial coronal plates is not 



I 



