1888.] NATURAL SCIENCES OF PHILADELPHIA. 353 



directed interradially. In two species of MiUericrinus rudimeutaiy 

 Underbasals have already been found by De Loriol/ and in both of 

 them the plates in question are attached to the top stem joint. 



From these facts we may fairly say that the dicyclic plan prevails 

 far more generally among Neocrinoidea than among Palaeocri- 

 noidea. 



It is very interesting to note, in this connection, that the under- 

 basals in many of the Ichthyocrinidaeare of an exceedingly rudiment- 

 ary nature. In IcJithyocrinus they are scarcely ever seen at all, being 

 usually visible only on the interior of the dorsal cup. In Taxocrimis 

 they are always hidden by the column, and sometimes visible only 

 within the calyx, which led Schultze to call them " cryptobasalia. " 

 In Forbes iocrmus and Onyehocrinus they are nearly always concealed 

 by the column, and furthermore in some cases they seem to be fused 

 with the upper joint of the column, for they separate from the 

 basals and remain attached to the column when the latter is broken 

 off. It is thereftTre a suggestive fact that in 3f{llericriniis polydactylus 

 and 3f. Orhlgnyi, the two species in which De Loriol discovered 

 underbasals, these were in a precisely similar way separated from the 

 basals and firmly attached to the column. 



Another distinction relied on by Carpenter is that in Neocrinoids 

 " by far the greater number of genera have five equal and similar 

 basals, with five equal and similar radials resting upon them. " He 

 excepts Syocrimis, which has three basals, and Ho/opus and Eudesi- 

 crinus in which the radials are not symmetrical; and he adds: "but 

 this want of symmetry is not due to the intercalation of any anal 

 plates as in nearly all Palaeocrinoids. " He therefore admits a certain 

 amount of asymmetry in Neocrinoids, so long as not due to anal ])lates, 

 though he elsewhere attaches some importance to a similar irregularity 

 in some Palaeocrinoids, when confined to basals and radials only, and 

 not in any way connected with anal plates, as for example Eucalypto- 

 crinus? 



Another point characteristic of the later crinoids brought out by 

 Carpenter is that " the articular flicets of the first radials occupy the 

 whole width of their distal faces, so that the lowest parts of the rays, 

 whether divided or not, are of nearly the same width as the radial 

 plates which bear them (Chall. Rep. p. 155). Exceptions to this are 

 found in Hyocrinus, Plicatocrinus and Marsupites. It is true that 



1 Paleont. Franc, Vol. XI, Crinoides Pts. 110 and 116. 



2 Challenger Report, p. 151. 



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