MORPHOLOGICAL PART. 61 
tion toward the proximal ring of plates visible in the calyx as that of Milleri- 
crinus and Apiocrinus, except that in the two latter the space above the top 
stem joint is vacant, while in Graphiocrinus it is filled by very small infrabasals 
(compare Fig. 17 with Fig. 20 on Table A). 
Small infrabasals are known to exist in the base of the Pentacrinoid genus 
Extracrinus, and de Loriol has discovered similar plates in two species of 
Millericrinus (Plate VI. Figs. 1 a, 6, and 2a,b). Those of AW. polydactylus he 
describes as follows:* “Je distingue trés nettement, sur deux individus, 
cinq piéces extrémement petites, 4 peime distinctes & Vceil nu, qui sont 
logées au centre de l’article basal, chacune reposant sur le sommet de I’une 
des carénes, dans une direction radiale, au centre se trouve, une petite 
dépression qui forme le fond de la cavité. Ces petites piéces, que je 
n’avais jamais encore observées, jouent évidemment le role de pieces infra- 
basales, mais & l'état tout a fait rudimentaire.’ Similar pieces were dis- 
covered by him in his M. Orlignyi, of which he says: + “ Elles ne peuvent 
absolument se voir que lorsque, par un hasard heureux, l'article basal peut 
se dégager du calice. Il me parait indubitable que se sont la de petites 
pieces infrabasales rudimentaires semblables 4 celles que j'ai signalées dans 
le M. polydactylus.” 
Admitting these plates to be infrabasals, it is certainly quite improbable 
that other species of Millericrinus having a pentangular stem, and those with 
a round stem, and the species of Apiocrinus,—a genus which, according to de 
Loriol, is very closely allied to Millericrinus and Guettardicrinus —- should have 
possessed no infrabasals. In all species of Millericrinus, the column, unless 
it is round, has interradial angles (Plate VI. Figs. 1%, 3, 4”, 5), exactly as in 
M. Orbignyi and all dicyclic Paleeocrinoids; and hence, if the genus were not 
dicyclic, this structure would be at variance with that of other Crinoids. We 
come to the same result if we examine the vacant space within the basal 
ring. This is radial, and disproportionate in size to the axial canal of the 
stem, which is small and circular; whereas if it represented the axial canal 
of a monocyclic Crinoid it should be interradial. The space is large enough 
to have contained, besides the canal, additional plates, which, if present, 
would have occupied the same position as the infrabasals of ML Orbignyi. 
The column of dicyclic Crinoids abuts either entirely against the infra- 
basals, or partly also against the basals. The latter is the case with the top 
* Paléont. Frang., lt série, Animaux Invertébrés, Terr. Jurassic, Tome XI. Premitre Partie, Crinoides, 
Paris, 1882-1884, p. 553, Plate 110. Figs. ] and 2. 
+ Ibid., p. 566 (Plate 116, Fig. 1, 4, c, d). 
