304 PROCEEDINGS OF THE ACADEMY OF [1885. 



divisions, and cover the greater part of the ventral surface up to 

 the summit plates, or the whole of it including the latter. The 

 free anus are simple or branching, and with a few exceptions 

 biserial. uniserial only in their immature state, permanently only 

 in a few Silurian genera. The articulation of the arms is primitive, 

 and dorsal canals have never been observed. All have pinnules, 

 which as a rule are closely folded together. The anus is sur- 

 rounded by solid plates, suturally connected; its position is 

 excentric, except in the Eucalyptocrinidse. 



The summit plates are largely developed, and consist in all 

 Carboniferous, and in most of the Devonian genera, of an undi- 

 vided oral plate, proximals, and frequently one or more radials ; 

 in most of the Silurian forms, however, of orals only, and even 

 these may be covered b}^ interradials. The disk is subtegminal, 

 but sometimes the covering pieces enter the outer surface, when 

 they lake the condition of surrounding plates. The Camarata 

 have small openings along the brachial zone, by means of which 

 the water for respiration entered the body. 



To the Articulata we refer all Paloeocrinoidea in which the 

 test is pliable. The calyx extends to the lower arm joints, and 

 the plates are united by articulation, and not by suture. Under- 

 basals are always represented ; they are small, being frequently 

 covered by the column, and consist of either three or five plates. 

 The number of primary radials varies from two to seven or more, 

 and also the number of the higher orders is very variable. The 

 radials of different rays are either in contact laterally or connected 

 by the help of interradials. In the former case, frequently, a 

 smaller number of radials alternates with a larger one, and the 

 plates of one ray rest with their upper sloping sides against 

 the lower sloping sides of their fellows of adjoining rays, or vice 

 versa. When the radials are separated by interradials, these 

 either extend to the basals, or rest against the upper sloping sides 

 of the fust radials. In some cases, however, the interradials are 

 restricted to tin? ventral surface. The form of the calyx varies 

 from almost strictly pentamerous to bilateral S3'mmetry, but it 

 sometimes becomes irregular, owing to the interposition of an 

 azygous plate. Some species have no anal plate dorsally. The 

 radial ami arm plates are united horizontally by muscles and 

 ligament, or perhaps in some case ^ li\ ligament only. The Lateral 

 face of the radials and those of the interradials are provided with 

 deep ligamental fossa?. The arms are closely folded together, 



