THE CRINOIDEA 129 



As fresh facts kept coming to light there was a good deal of 

 shifting of ground and mutual criticism on the part of Wachsmuth 

 & Springer and Carpenter. The supposed difference, and con- 

 sequently the classification, were rejected by Neumayr (1889) and 

 Bather (1889-90). Independently and synchronously Wachsmuth 

 & Springer (1889) concluded, chiefly on the evidence of Taxocrinus 

 intermedius (p. 126), that " in some Palaeozoic crinoids-the mouth is 

 exposed, and there is no vault aside of the orals " ; also that " all 

 attempts to subdivide the Crinoidea by separating the Palaeozoic 

 from the Mesozoic and later forms as natural divisions will have 

 to be abandoned." But it was not till 1891 that they published 

 their recantation of the view that " the Camerata had a vault and 

 a subtegminal disk." 



The explanation of the Camerate tegmen given by Wachsmuth 

 & Springer in 1891 was readily accepted and now prevails. It 

 may be condensed as follows : The plates of the tegmen were at 

 first small and yielding, as in the Ichthyocrinidae and in most 

 recent crinoids ; in this state when the arms are open the ventral 

 surface is depressed, when they are closed it bulges upwards. To 

 afford better protection to the viscera the tegminal plates became 

 more solid ; the tegmen being thus less flexible was fixed perforce 

 in its protruded state. The covering-plates of the ambulacra had 

 perhaps been closed from the begin- 

 ning, but as, through the upswelling of 

 the tegmen, the grooves were now more 

 exposed, further protection was needed. 

 Consequently they were lowered be- 

 neath the surface and, starting from 

 the solid orals, interambulacral plates 

 closed in over them. Certain of the 

 covering- plates, however, especially, 

 it would appear, the axillary pieces, 

 which perhaps could not so easily be 

 covered by other plates, became much 

 stouter, and were still exposed on the 

 surface as solid radial dome-plates. In FlG - XLIV - 



any form highly developed along these 

 lines, e.g. Cactocrinus (Fig. XLIV.) the 



food-grooves, Water-Vessels, and blood- one side of tegmen broken away, 



i i , v ,1 4.1.-. showing how the food-canals pass from 



Vessels are SUnk right beneath the the arm - openings (Br r ) under the 



farrmon anrl ova onnlncArl in a tnViP tegmen to the upper end of the con- 



tegmen, and are enclosed m a tuc , vo i u ted organ (after F. B. Meek, ms). 

 consisting of alternating ambulacrals x . 2, one of the food-canals, from 



., Till i j i above, further magnified (after Meek). 



above and adambulacrals or side-plates 3, the convoluted organ, from below. 

 below. The interambulacral plates of 



the tegmen send curious extensions into the interior of the calyx, and 

 these extensions, spreading out, form what used to be regarded as 



