SILURIAN RADIATA. 167 



longitudinally ; the sulci corresponding to the divided edges 

 of the lamellse, leaving one of the equal intervening ridges to 

 correspond with each of the spaces between the individual 

 lamellae, and between their divided edges. 



This is the only species of the genus I am aware of in the 

 Silurian rocks. 



Rare in the Upper Ludlow rock of Underbarrow, Kendal. 

 [Col, University of Cambridge.) 



Spongarium cequistriatum (M'Coy). 



Sp. Char. Elliptical, depressed, proportion of width to length 

 varying from 85 or 90 to 100 ; marked with sharp, rugged 

 concentric wrinkles ; entire disk closely and evenly radiated by 

 coarse rounded very approximate ridges, averaging five in 1 line. 

 Long diameter from 8 lines to 1 inch. 



This species is perfectly distinguished from its congeners by 

 the coarse, close, equal striation of the entire disk, giving it a 

 peculiarly harsh aspect ; the ridges are much less than their thick- 

 ness apart. 



Rather rare in the quartzose Upper Ludlow rock of Benson 

 Knot, Kendal. 



{Col. University of Cambridge.) 



Spongarium interlineatum (M'Coy). 



Sp. Char. Broad oval, usual proportion of width to length as 

 85 to 100, marked with very strong concentric tmdulations ; 

 radiating ridges very numerous, straight, slender, simple, of 

 unequal lengths, averaging with considerable regularity half 

 a line apart; intervening spaces finely striated radiatingly; 

 long diameter varying from 7 lines to 1 inch 3 lines. 



This species is easily distinguished from the S. Edwardsi 

 (Murch.) by having considerably more than double the number 

 of radiating ridges ; they have never been seen to dichotomize, 

 but retain their comparatively near approximation by the inter- 

 calation of similar, straight, shorter ridges towards the circum- 

 ference ; the substance also appears stronger and is more strongly 

 wrinkled concentrically; the small radiating striae between the 

 larger ridges are very characteristic. 



One very obscure specimen, apparently of this species, measures 

 2 inches in its long diameter ; the distance between the main 

 ridges is about four times their thickness. 



Abundant in the green micaceous quartzite of the Upper Lud- 

 low at Benson Knot, Brigsteer and Scalthwaiterigg, Kendal. 



(Col. University of Cambridge.) 



