210 ME. W, PEECT SLADEN ON THE 



Htmenastee, Wyville Thomson. 

 Synopsis of Species herein described. 



A. One ambulacra! spinelet. 



t Paxillse-crowns forming raised areas of membrane.. .1 , .,. 

 Spiraeula small, numerous, equidistantly spaced . . . ) ™''**"*- 

 tt Paxillse-crowns not forming raised areas. 



1. Spiraeula single, large, uniformly spaced formosus. 



2. Spiraeula in groups of 6-10, small, irregularly 



distributed pergamen- 



[taceus. 



B. Two ambulacral spinelets. 



t Muscular fibrous bands of dorsal membrane coherently 

 reticulated. 



* Paxillae-crowns forming definite areas. | 



Spinelets not prominent. j saeeulatus. 



** Paxillae-crowns not forming definite areas. 

 Spinelets very prominent. 



1 . Spinelets forming a raised keel over each radius. I t. • , , 

 Spiraeula large, single, distributed. \ ^('^^^^^lO'tus. 



2. Spinelets not forming a raised keel. ( 

 Spiraeula microscopic, in groups of 10 or more, j ^ *^** 



tt Muscular fibrous bands of dorsal membrane simply 

 intercrossing. 



* Radial areas elevated in relief above the inter-) 



brachial tissue. \ glaucus. 



Paxillse with three spinelets. j 



** Radial areas not elevated above the interbrachial 

 tissue. 

 Paxillse with more than three spinelets. 



1. Radii broad. Aperture-papillse simple vicarius. 



2. Radii attenuate. Aperture-papillse comb-like. . infernalis. 



C. Three ambulacral spinelets. 



t Muscular fibrous bands close, subdiffused, coherently 

 reticulated. 



* Paxillse-crowns forming definite areas in relief. 



1. Paxillar elevations closely crowded. I , 

 Spiraeula uniformly distributed, not in lines, j '^^ ^ ''*• 



2. Paxillar elevations widely spaced. [lines. I .» 

 Spiraeula confined to interspaces, arranged in j ■^^ ' 



** Paxillse-crowns not forming definite elevated areas. 



a. Ambulacral spines partially webbed. 1 , 



i hree pairs oi secondary mouth-spines, j 

 /3. Ambulacral spines not webbed. 



Two pairs of secondary mouth-spines. 



1. Meshes of dorsal membrane irregular and 1 



not uniform. I latebrosus. 



Ambulacral spines unequal. J 



2. Meshes of dorsal membrane small andl 



uniform. > porosissimus. 



Ambulacral spines equal. ) 



tt Muscular fibrous bands fine, definite, widely spaced, 

 simply intercrossing. 



* Dorsal membrane with granular bodies graniferus. 



** Dorsal membrane devoid of granular bodies. 



a, Ambulacral spines long and needle-shaped. . geometricus. 



