EEPORT ON THE CRINOIDEA. 183 



portion of the vault." ^ I have seen a similar arrangement in well preserved specimens of 

 Marswpites, while both d'Orbigny ^ and de Loriol have figured and described the same 

 thing in Apiocrinus roissyanus. After stating that there is a considerable amount of 

 variation in the interradial areas, even in the same individual, de Loriol says — " Presque 

 toujours la serie commence par une piece unique, hexagone on 

 heptagone, qui est la plus grande, et se trouve encastree entre les ^j i^' 



premieres et les secondes radiales, de chaque cote, reposant sur les '~\ 



troncatures des premieres radiales. Au-dessus il y a deux, trois, b, .ifPl 



et meme quatre pieces plus petites, irregulieres, polygonales, qui - _ ';V 



arrivent au niveau des facettes articulaires des troisiemes radiales, B;' ^ '' , Vl 

 une troisieme et une quatrieme rang^e comprennent encore chacune ^ 

 trois ou quatre pieces polygonales plus petites, et occupent I'espace 

 entre les premiers articles brachiaux ; elles sont suivies par d'autres 

 rangees de pieces, plus petites encore, qui paraissent concourir a la 



I, .- T, A, 1 •. T • 1 " 3 "n T • l> FiG- 9- — Interradial plates of 



formation dune voute sur la cavite calicmale. De Loriol s Apiocrinus roissyanus 



enlarged representation of this structure is reproduced in fig 9. first and second brachials- 



, 1 „ Ti • Til Rl, R2, K3, first, second, 



Here, surely, there was a "dome as solid as m any Ichthy- and third radiais; pi, 



■^ _ . basal joints of lowest 



ocrinoid ; but it will scarcely be contended that this dome pinnule; /, caiyx-inter- 



•^ _ _ radial, resting on the 



rem'esents the heavy rigid vault of Actinocrinus, rather than the "pp^^ angles of two first 



-T ^ D ' radials (Rl) ; i, smaller 



plated ventral perisome of recent Pentacrinidse and Comatulidse. interradiais, but probably 



r J. only pensonuc plates. 



The former range back to the earliest Mesozoic times, long anterior 



to Apiocrinus ; and the Liassic Extraainus had a vault essentially similar to that of the 

 Apiocrinidse. But there was no regular calyx-interradial resting upon the upper angles 

 of the first radials. Its place was taken by a number of movable irregular perisomic 

 plates, lilie those which occur in the same position in Pentacrinus asterius (PI. XITL 

 fig. l). They are represented by Miller,* Austin, and also by Quenstedt;^ and were 

 continued upwards into those " which cover the dome-like integument over the abdominal 

 pouch,'' just exactly as is the ease with their fellows in recent forms. 



The Silurian genera Glyptocrinus, Reteocrinus, and Xenocrinus appear to me to have 

 been in the same condition ; though I will not go so far as to say that the mouth was 

 open to the exterior. For the peristome may well have been closed by the more or less 

 well defined apical dome plates, which covered the central part of the disk, just as in the 

 Ichthyocrinidae. The vault of Glyptocrinus is best known in Glyptocrinus decadactylus. 

 According to Miller' "The regular interradial areas have one plate resting upon the 

 primary radials, two in the second range, three in the third, two or three in the fourth, 



1 Revision, part i. p. 54. " Eist. Nat. des Crino'ides, p. 21, pi. ill. figs. 1, 3. 



3 Paleont Frang., loc. cit., pp. 272, 273. * Op. cit, pp. 57, 59. 



» Encriniden, Tab. 101, fig. 39a. * Austin, op. cit., p. 104, pi. xiii. figs, la, Ic, Ih 



' Glyptocrinv^ redefined and restricted, Gaurocrinus, Pycnocrinus, and Compsocrinus establislied, and two new 

 species described, Joum. Cincinn. Soc. Nat. Hist., vol. vi. pp. 220, 221. 



