REPORT ON THE CRINOIDEA. 145 



X.— ON THE RELATIONS OF THE NEOCRINOIDS TO THE 



PAL^OCRINOIDS. 



The term " Neocrinoidea," which was first introduced by the writer in 1881/ embraces 

 all the " Crinoidea Articulata " of Miller and Miiller, together with Marsupites and Holopus, 

 both of which were placed elsewhere by the German zoologist ; while the Palaeozoic 

 Crinoids generally were referred to by him as the " Crinoidea Tessellata," ^ this group 

 includins the Semiarticulata and Inarticulata of Miller. His definitions of these two 

 great groups, however, were meagre in the extreme. The Articulata comprised the genera 

 Pentacrinus, Apiocrinus, Encrinus, and Comatula in the wide sense, i.e., types in which 

 the radii are free down to the base of the calyx ; while his only distinct reference to the 

 Tessellata is that they are Crinoids " deren Kelch ganz aus Tafeln zusammengesetzt ist." ^ 

 From his numerous references to individual genera, however, it is possible to obtain a 

 tolerably clear notion of the ideas which led Miiller to establish these two principal 

 divisions of Crinoids ; and various palaeontologists have in consequence attempted, with 

 more or less success, to formulate characters which should distinguish them from one 

 another. 



The most satisfactory of the earlier attempts in this direction was that which appeared 

 in Bronn's Thierreich (vol. ii. p. 228). Besides the supposed sutural union of the calyx- 

 plates and the presence of a subtegminal mouth in the Tessellata, reference is also made 

 to the asymmetry of the calyx in this group, the more frequent presence of a dicyclic 

 base, and the greater rarity of stemless forms than in the Articulata. 



On the other hand, Liitkcn'' and others have pointed out the weakness of these 

 definitions. 



By far the best of the numerous diagnoses which have been drawn up since the time 

 of Miiller are those which we owe to Zittel.^ But the freedom of the rays in the Articulata, 

 on which Miiller laid stress, is omitted Ijy him, while an important error runs through his 

 as through all the earlier definitions. The calyx plates of the Tessellata are " unbeweglich 

 durch einfache Nahte verbunden ; " while those of the Articulata are " meist sehr dick, 

 durch gelenkartig ausgehcihlte und gewolbte oder ebene Nahtflachen verbunden." Now 

 the lowest articulation to be found in the calyx of an articulate Crinoid is that which 

 unites the first and second radials (PL LXIL). The former are suturally united both to 

 one another and to the basals ; while, when underbasals are present (Marsujntes, 

 Extracrinus), the union between them and the basals is of the same kind. In both 

 groups the interradials (when present) are suturally united to the radials and to one 

 another ; so that the name-giving difference between the Articulata and the Tessellata is 



1 Ann. and. Mag. Nat. Hist., 1881, ser. 5, vol. vii. p. 296. ^ Pentacrinus, he. cit., p. 30. ^ md., p. 29. 



* Op. cit, pp. 219-222. ^ PaliBontologie, pp. 335, 342, 345. 



(ZOOL. CHALL. EXP. — PART XXXII. 1884.) Ii 19 



