and Species of Crinoidea. 203 



divide, each branch ending at the base of the rays. All the 

 perisomic plates are radiated. Abdominal plates small and 

 mammiform. Mouth lateral. Rays forty. Columnar joints 

 alternately thicker and thinner. 



R. granulatus, Austin, sp. 

 Def — Perisomic plates agree as to number and arrange- 

 ment with the generic type, but instead of elevated ribs, as in 

 the last species, the same end — strength — is attained by the 

 superior thickness of the plates lying in the line of the rays. 

 In consequence of this increased solidity, these plates are more 

 elevated than the adjoining ones, the elevations being greatest 

 in their centres. All the perisomic plates are minute, elevated, 

 and finely granulated. Mouth lateral. Rays probably twenty. 

 Columnar joints alternately larger and smaller. 



Genus Tetramerocrinites*, Austin. 

 Def, — Dorso-central plates four, pentagonal. First series 

 of perisomic plates eight, four of which are heptagonal, and 

 the remaining four pentagonal, alternating with each other ; 

 second series or ray-bearing plates eight, with a double exca- 

 vation in each for the insertion of the ray-joints ; several in- 

 tervening plates occur, but the number is unknown. 



T. formosus, Austin. 

 Def — Little is known of this species beyond the descrip- 

 tion given in the generic definition. The unique specimen 

 obtained of this species departs from the usual quinary type 

 in the arrangement of its rays, which are in four groups of 

 four each, instead of five, as is more generally observed in the 

 Crinoidea. The depressions in the quadripartite dorso-central 

 plates for the attachment of the column are small but deep. 

 The body plates are all beautifully radiated from their centres. 

 Column and rays unknown. 



Family Periechocrinites^ Austin, 

 comprising the genera Periechocrinites and Sagenocrinites. 

 Genus Periechocrinites, Austin. 

 Def — Dorso-central plates three. It is difficult to define 

 the perisomic plates in this genus in the same manner as in 

 other genera, because they do not occur in regular series as in 

 Actinocrinites, but are regular only in the line of plates which 

 run from the dorso-central plates to those bearing the rays. 

 These may be considered as the principal plates, as they are 



* From tetrameres, consisting of four parts, f From periecho, to surround. 



