186 ECHINODERMATA— PELMATOZOA phylum iv 



covered ; the covering pieces of the latter frequently incorporated in the tegmen. Anal 

 opening eccentric or subcentral, frequently situated at the end of a proboscis-like anal 

 tube. Arms uniserial or biserial, and jnnnulate. Ordovician to Carboniferous. 



In some of the earlier (Ordovician) forms, as in the Reteocrinidae and 

 Batocrinidae, there is considerable flexibility in the tegmen, which is com- 

 posed of innumerable small plates ; but the mouth and food grooves in all 

 these are perfectly subtegminal, thus distinguishing them from the Flexibilia, 

 some of which, in respect to flexibility of the tegmen, they superficially 

 resemble. 



Family 1. Cleiocrinidae. 



Dicyclic. Brachials to height of several orders incorporated in calyx by lateral 

 union, those of different rays in contact except at the anal side. Calyx plates furnished 

 with pore-rhombs crossing the sutures as in some Cystoidea. Arms jnnnulate. Tegmen 

 of small undifferentiated plates. Mouth subtegminal. Ordovician. 



C/eiocrwrns Billings (emend.). Calyx large, pliant; plates joined by loose 

 sutures, crossed by pore-rhombs. IBB five, invisible exteriorly. Basals and 

 radials not in typical succession, but alternating with each other in a 

 horizontal ring of ten plates surrounding the IBB and projecting downward 

 over the column like a collar. No iBr except at the anal side ; anals in 

 vertical series, resting on the truncate posterior basal, and extending high up 

 between the rays, Rays and their divisions up to the free arms contiguous 

 and interlocking ; brachials bifurcating several times in the calyx, giving off ' 

 fixed pinnules, which are incorporated by lateral imion with adjacent brachials 

 and become free between the arm bases. Arms small, uniserial and 

 unbranched. Column obtusely pentagonal, or nearly round. Lowest 

 Ordovician (Chazy and Trenton) ; Canada and the United States. 



Tills genus has the flexible calyx and loose sutures of the Flexibilia, but its pinnulate 

 arms and subtegminal mouth place it in closer relation with early Camerata, such as 

 Eeteocrinus. Its calycine pore-rhombs proclaim its not distant derivation from the Cystitis. 

 In the remarkable disposition of the basal and radial plates, in horizontal alternation instead 

 of vertical succession, touching the infrabasals by their exterior surface instead of the distal 

 edge, this form differs from all known Pelmatozoa. These intermediate and peculiar 

 features accord with its very early age. 



Family 2. Reteocrinidae. Waclismutli and Springer (emend.). 



Dicyclic. The lower plates of the rays more or less coiapletely separated from 

 those of other rays, and from the primary interradials, by irregular supplementary 

 pieces, without definite arrangement. Anal interradius divided by a vertical row 

 of cons])icuous plates. Ordovician. 



Beteocrinus Billings (em. W. and Sp.). Dicyclic. IBB five, variable. EB 

 and fixed brachials folded into a strong median ridge, which follows the 

 bifurcations and passes insensibly into the arms. A similar ridge of anal 

 plates divides the posterior interradius, extending to the anal opening. 

 Radials separated all around. Arms usually branching; uniserial, or with 

 interlocking cuneate ossicles. Interbrachial areas filled with innumerable 

 minute pieces forming an apparently pliant integument continuous with the 

 tegmen. Column round or pentagonal. Ordovician (Trenton to Cincinnatian) ; 

 North America. 



