186 ECHINODERMATA— PELMATOZOA phylüm- iv 



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

 opening eccentric or subcentral, frequentUj situated at the end of a prohoscis-like anal 

 tube. Arms uniserial or hiserial, and pinnulate. 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 distingirishing them from the Flexibilia, 

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

 resemble. 



Family 1 . Oleiocrinidae. 



Dicydic. Brachials to height of several orders incorporated in calyx hy lateral 

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

 with pore-rhomhs crossing the sutures as in some Cystoidea. Arms pinnulate. Tegmen 

 of small undifferentiated plates. Mouth subtegminal. Ordovician, 



Cleiocrinus Billings (emend.). Calyx large, pliant ; plates joined by loose 

 sutures, crossed by pore-rhombs. IBB five, invisible exteriorly. Basais 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 union 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. 



This genus has the flexible calyx and loose sutures of the Flexibilia, but its innnulate 

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

 Reteocrinus. Its calycine pore-rhombs proclaim its not distant derivatiou from the Cystids. 

 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 diff"ers from all known Pelmatozoa. These intermediate and peculiar 

 features accord with its very early age. 



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



Dicydic. The lower plates of the rays more or less completely separated from 

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

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

 of conspicuous plates. Ordovician. 



Reteocrinus Billings (em. W. and Sp.). Dicydic. IBB five, variable. PiR 

 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. 



