HISTOEICAL. . 29 



tegmen consists of ^ye large pieces, as in ITaplocrinus, etc., these plates are 

 orals, and not supplementary pieces as we had supposed. 



The logical consequences of these conclusions were taken up by us in 

 1890,* when we undertook to prove that the so-called vault of Palaeozoic 

 Crinoids is not a structure sui generis, but a highly differentiated disk ; that 

 their large, rather regularly arranged interbrachial and interambulacral 

 plates represent morphologically the smaller irregular pieces between the 

 rays and ambulacra of later forms, and that the Palaeozoic and Neozoic 

 Crinoids do not differ so essentially from one another as we had supposed. 

 It also appeared that neither the closure of mouth and food grooves, nor 

 the presence of anal plates, is a constant character among the older Cri- 

 noids, and we were compelled in 1888 to abandon the Palseocrinoidea and 

 Neocrinoidea as systematic groups. 



That the two groups could not be upheld, was proved also by Neumayr,t 

 who claimed that none of the characters by which they had been separated 

 was persistent ; and he proposed in place of them a primary division based 

 upon the condition of the mouth and ambulacra, whether suUegminal or 

 siiprategminal, viz. : 



I. Hypascocrinoidea. Mouth, ambulacral vessels, and Saumplattchen (tlie latter if pres- 

 ent) beneath the tegmen. 



1. Sjjhceroidocvinacea. Cup mostly, tegmen always, constructed of a large number of 



plates immovably connected among themselves. Generally several of the arm 

 plates incorporated into the calyx by means of interradial pieces. Tegmen roof- 

 ing the whole ventral surface. Among its plates are readily distinguished a 

 central one, and four and two interradial proximals. Anus either directly piercing 

 the tegmen, or placed at the terminal end of a plated tube. (This group agrees 

 with our Camerata.) 



2. Haplocrinacea. Cup and tegmen composed of a small number of immovable pieces. 



The former having but one radial, and no interradials except an anal. Tegmen 

 with a central plate. (Our Larviformia.) 



3. Ichthyocrinacea. Cup and tegmen composed of very numerous, somewhat movable 



pieces; the former having two basal rings and more than one order of radials. 

 (Our Ichthyocrinidse.) 

 II. EpasGocrinoidea. Ambulacra not covered by the tegmen; their furrows exposed or 

 closed by Saumplattchen. 

 1. Cyatliocrinacea. Base generally dicyclic. Cup without interradials at the four 

 regular sides. Tegmen, so far as known, composed of five orals, which support at 

 their edges the ambulacra; the latter covered by Saumplattchen. Anus within the 

 ventral sac. (Our Fistulata.) 



* Perisomic Plates of the Crinoids (Proceed. Acad. Nat. Sci. Phila., October, 1890, pp. 345-375). 

 t Die Stamrae des Thierreiches, Wien und Prag, 1889, pp. 438-460. 



