TRICIIOTASTER. 



169 



obtuse ; marginal plates rounded, and diminishing gradually in size from the angle to 

 the apex. Each marginal plate appears to have supported on its upper surface a 

 thorny spine, which projected obhquely backwards. 



On Trichotaster, a New Genus of Silurian Asteroidea. 



On the 26th March, 1873, Dr. Grindrod, of Malvern, forwarded to me some Silurian 

 fossils to examine and determine for him. 



On one of the slabs I discovered a remarkable little Starfish on a fragment of 

 Wenlock Limestone from Dudley, forming a new genus of the order Asteroidea. 



Genus — Trichotaster, Wright, 1873. 



Small Starfishes with a large disk, the structure and clothing of which are unknown, 

 this part being absent. Rays numerous, short, lanceolate, and closely surrounding the 

 disk in a stellate fashion, the border of each armed with small triangular dentiform spines ; 

 from the extremity of each ray a stem-like multi-articulate process proceeds, equal in 

 length to the ray itself. The outer rings of this process support slender-jointed lateral 

 appendages, imparting a tuft-like character to the terminations of the rays. 



Trichotaster pltjmiformis, Wright, n. sp. 



Body oblong, rays ten, unequal, the side of each border surrounded with from eight 

 to ten separate, sharp, triangular, dentiform spines. 



The terminal stem, consisting of eight joints, of which the four outer or last-formed 

 support two slender, lateral, antennaeform processes ; the length of these diminish from the 

 proximal to the distal pair, and produce by this arrangement a beautiful plume-like 

 structure at the termination of each ray. 



Dimensions. — Disk, greatest diameter four- tenths of an inch. Lesser diameter three 

 tenths of an inch. Length of one ray, with its terminal plume-like process, three-tenths 

 of an inch. 



Locality and Stratigraphical Position. — Imbedded in hard grey Wenlock Limestone 

 from Dudley! I have only seen the one specimen now described. 



