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H li | : «648 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
PIE BEN | | 
i | “margins. The distichals, and all the higher orders of brachials to the last 
) | ! | | bifurcation, generally consist of two plates each,* of which the upper one is | 
VP | fi axillary. These plates have the form of free arm plates, being rounded on the 
| { Hl it ! | back, but the lower ones are suturally connected with the plates of the disk, | 
| ‘ i ‘| | and in some species also with the radials, or with their fellows of the <4 
' i t| | opposite side of the ray, and are therefore rigid. The rays divide above | 
mii iid KH the costals into two branches, which bifurcate independently, the axillaries of 
| ali | | both branches bearing an arm upon one side, and the next order of brachials 
| i ' | upon the pimonikc side, ue last eatery SuNBONED two arms. felpetlies : | 
Kt vy strong, the first pinnule given off in some species from the first distichal, 
1? iW | | in others from the proximal arm plate. | 
fi \ il i : : Ventral disk pyramidal, convex, or almost flat. Orals slightly excentric, | | 
ik | i | i | and more or less asymmetrical. Ambulacra composed of two series of cover- 
ie | \ i | ing pieces, which are exposed upon the disk. ‘The interambulacral plates | 
I ul} i? | variable in number, except the first row, which in part is ne Koad eave and | 
eh | | | always consists of three plates transversely arranged. The middle one of | 
| ; VAN | a) | these plates is larger than the two at the sides, which are elongate and bend | 
iB | | | | outward to form the ambulacral passage. The upper ends of the side plates | 
a HTH rest against the covering-pieces of the ambulacra, the lower ends against the | 
if | i | | sides of the costals or distichals, as the case may be, and sometimes against | 
| ‘ \ ) N the palmars. The anal side has also three plates in the first row, of which, 
| (ih : as a rule, the middle one is widest and sometimes higher than the corre- = 
al) | sponding plates of the regular sides; these are followed by numerous small | 
(i! fe 14h plates. Anus excentric, either opening out directly through the disk, or | 
i) K ; | located at the top of a protuberance, sometimes at the end of a tube. | 
\ a ial Column of moderate length, the lower end giving off rootlets at irregular | | 
( ai a intervals; the joints elliptic and twisted, the twist being imparted to the | 
| i ‘| Hi whole stem, permitting motion in all directions. The articulation between | 
i 4 the joints bifascial, there being a well defined ridge following the long | 
Ve | iN diameter of the joints. Axial canal very small. 
. 4 i Distribution. — This genus constitutes one of the leading fossils of the | 
iil MI Subcarboniferous on both sides of the Atlantic. It made its appearance in 
yi il the Hamilton group, and became extinct in the St. Louis, reaching its 
| i} 1 f | climax in the Lower Burlington limestone, from which horizon we recognize 
| \ twenty-eight species, not counting the numerous synonyms. 
" it es In P. incomptus, and some others, representing a transition toward Eucladocrinus, the orders of 
if | | ‘| brachials above the palmars consist of three successive plates. 
Mi | NI 
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