on British Falreozoic Crinnids. 293 



when tliey may be fitly replaced by other names which are 

 less misleading in their character. 



According to Miiller's original definition *, the articulate 

 Crinoids are those in which the radii are free down to the 

 base of the calyx. They do not meet laterally ; but the in- 

 tervals between them are filled by perisome continuous with 

 that of the ventral surface of the disk, and either bare or 

 plated. Liitken has pointed outf that, according to this 

 definition, the Mesozoic Apiocrinus and Ouettardicrinus can- 

 not be included among the Articulata. In the former the 

 second and third radials are united with their fellows all round 

 the calyx by interradial plates, while in the latter the rays are 

 united as far as the second arm-joints, either directly or by 

 interradial plates. The same is the case in many recent 

 Comatulce. On the other hand the rays of the Palasozoic 

 laxocrinus were just as free as those of Pentacrinus ; and this 

 genus entirely corresponds to Miiller's definition of the Arti- 

 culata. The same may be said of other so-called " tessellate 

 Palajocrinoids." 



An attempt has also been made to separate the Mesozoic 

 Articulata from the Palseozoic Tessellata on the ground that 

 the successive radial plates of the latter are only suturally 

 united, while in the former group they articulate upon one 

 another. Here again, however, Gnettardicrinus and Apio- 

 crinus are tessellate though not Palasozoic Crinoids. Further, 

 in many of the Palffiocrinoids the distal faces of the first or 

 second radials are true articular surfaces in which the fossge 

 for the insertion of muscles and ligaments are much more 

 distinctly marked than in the corresponding joints of many 

 Apiocrinidaj, or even of recent Pentacrinidse. 



In spite of Liitken's well-grounded attack upon the 

 Miillerian classification, it has recently been entirely adopted 

 by Prof. Zittel \ on the ground that it " liefert vortrefflich 

 abgegrentzte natiirliche Gruppen." We cannot understand, 

 however, how Cyathocrinus^ Poteriocrinus^ Plafycrinus, and 

 Myrtillocrinus can find places in a group a leading charac- 

 teristic of which is that the plates of the calyx are " unbeweg- 

 lich durch einfache Niihte verbunden." It is obvious from 

 the context that vertical and not horizontal union is meant. 

 The latter occurs in all Crinoids as far as the first radials, 



* " Ueber den Bau des Pentacrinus caput- Medusce,^^ Abliandl. d. Ber- 

 lin. Akad. 1843, p. 25 (of separate copy). 



t " Om Vestindiens Pentacriner med nogle Bemaerkninger om Pen- 

 tacriner og Solilier i Ahuindeliglied," Videuskabelige Meddelelser fra den 

 naturhistoriske Porening i Kjcibeubavu, 1804, no. 13-10, pp. 220 seq. 



X Op. cit. pp. 342 and 345. 



