20 DUBLIN UNIVERSITY 



Diagnosis. — Calyx small, composed of five shield-like thick plates, 

 having a double excavation at their lower extremity, where they articu- 

 late with the pentagonal stem : radial plates five in number, about twice 

 as broad as long : brachial plates also five in number, broad and tri- 

 angular, supporting the rays, which are ten in number, and very long, 

 composed of cuneiform, alternating articulations, and bifurcating four 

 or perhaps more times, every alternate joint of these rays being furnished 

 with a long, slender, eight-jointed pinnule. The stem consists of a num- 

 ber of pentagonal joints of equal length, each united by a crenulated 

 margin, and for the greater portion of its length comparatively smooth, 

 but towards the calyx becoming strongly ridged, and beaded across the 

 exterior surface of each angle; at about every eighth joint on each of its 

 angles were articulated five closely-jointed ramules. 



DIMENSIONS OF SMALL SPECIMEN. 



Length of calyx, yL ; diameter, -fa of an inch. 



Diameter of stem rather less than T \j of an inch. 



Length of rays, about two inches, 1 . , , ,, , „ . 



° J > probably much longer when perfect. 



Do. of stem, nearly five inches, J 



DIMENSIONS OF LARGER SPECIMEN. 



Length of calyx, / n ; diameter, -^ of an inch. 



Diameter of largest fragments of stems, y 4 ^ of an inch. 



Other fragments vary in diameter, from rather less than y 1 ^ to -^ 

 of an inch. 



This fossil sea lily is remarkable for its elegant and graceful form and 

 the great length of its arms ; the calyx or cup, like that of the typical 

 and recent example of this genus Pentacrinus caput Medusce, is small, and 

 composed of but few plates, the basal series or pelvis consisting of five 

 very convex and solid elements, the lower portion of each being exca- 

 vated, forms an articulating surface which rests securely on the penta- 

 gonal stem ; the five radial plates are closely fitted to these ; upon them rest 

 the five brachial plates, triangular in form, the sides of which support 

 the long rays or arms, which bifurcate or subdivide several times ; these 

 are ten in number ; commencing from the brachial plate, they continue 

 for about y^ths of an inch to the first subdivision, consisting of from 

 eight to ten irregularly-shaped joints, closely fitting to each other, and 

 bearing a second triangular plate ; like the first brachial plate, the sides 

 of this support the second division, one branch of which, consisting 



