218 proceedings of the academy op [1886. 



Notes on the Underbasals and Top Stemjoint of Neocrinoidea 



AND PaL^EOCRINOIDEA. 



On p. 8 we stated that probably many Neocrinoids, heretofore 

 supposed to be monocyclic, either have small underbasals con- 

 cealed beneath the column, or that these plates had been repre- 

 sented in the early larva. We referred to the genera PentacrinuSy 

 Millericrinus and Apiocrinus, which, according to our generaliza- 

 tions on p. T, are built decidedl}^ on the plan of dicyclic Palseo- 

 crinoids. Our investigation, unfortunately, could be extended 

 only to comparatively few species, as the column and axial canal 

 of the Neocrinoidea very frequently, and even among the genera 

 to which we alluded, are not angular, and Pentacrinus among the 

 three is the only genus that has lateral cirrhi. 



Rudimentary underbasals are known to exist in the Pentacri- 

 noid genus Extracrinus, and similar plates have been discovered 

 in the ApiocrinidjB by Mr. De Loriol in two species of Millericrinus. 

 In these species, as in the case of Extracrinus, the angles of the 

 column, when this is pentangular, are interradial, the canals radial, 

 exactly as in species in which underbasals are supposed to be 

 wanting, but contrary to the conditions of monocyclic Palseocri- 

 noids in which the angles of the column are radial, the axial canals 

 interradial. 



Millericrinus polydactylus, according to Mr. De Loriol (Mono- 

 graph of the French Crinoids, p. 553, PI. 110, figs. 1 a and 2 ay, 

 has five minute plates within the basal ring, which were regarded 

 by him as " infrabasalia," the term which he applies to under- 

 basals. De Loriol describes these plates as follows : " Je distingue 

 trfes nettement, sur deux individus, cinq pieces extremement 

 petites, a peine distinctes a I'oeil nu, qui son logees an centre de 

 Particle basal, chacune reposant sur le sommet de I'une des 

 carfenes, dans une direction radiale ; au centre se trouve une 

 petite depression qui forme le fond de la cavite. Ces petites 

 pieces, que je n'avais jamais encore observees, jouent evidemment 

 le role de pieces infrabasales, mais a I'^tat tout a fait rudimen- 



1 By an error it was stated on p. 7 in Eule 2 : the five sections of the 

 column are "radial,^^ the longitudinal sutures " interradial," which should 

 read: the five sections of the column are "interradial," the longitudinal 

 sutures "radial." 



'^ This and the succeeding- quotations are made from the Palcontologie 

 Franqaise, Ire Serie, Animaux Invertebres, Terrain Jurassique, Tome xi, 

 Premiere Partie, Crinoides, par M. P. De Loriol, Paris, 1883-1884, 



