1886.] NATURAL SCIENCES OF PHILADELPHIA. 219 



taire." Similar pieces were discovered by him in his MiUericri- 

 nus Orhignyi (PL 116, figs. 1 b,Cjd), upon which he says on p. 

 566 : " Elles ne peuvent absolument se voir que lorsque, par un 

 hasard heureux, Particle basal pent se d^ager du calice. II me 

 parait indubitable que ce sont la de petites pieces infrabasales 

 rudimentaires semblables a celles que j'ai signalees dans le Hill, 

 polydactyhts.''^ 



We full}^ agree with the distinguished Swiss palaeontologist 

 that the plates in question in both cases are rudimentary under- 

 basals, from the very fact that the plates are disposed radially, 

 the outer angles of the column interradially, as seen in Hill. 

 Orhignyi^ in which the stem is pentangular. 



Admitting these plates to be underbasals, we doubt if all 

 other species of Millericrinus, which have an interradial pentan- 

 gular stem, and those with a round stem, and the species of Apio-- 

 C7-inus^ a genus which, according to De Loriol, is closely allied to 

 Miller icrinus, should be devoid of underbasals. In that case the 

 two species should be separated from the others, and be placed by 

 themselves under a very distinct genus. 



That small underbasals at least temporarily were represented 

 in other species of Millericrinus and in Apiocrinus, is indicated 

 by the fact that the open space within the basal ring, which in 

 Millericrinus Orhignyi is occupied by the underbasals, is radial, 

 contrary to the axial canals of monocyclic Palaeocrinoids, which 

 are interradial. Moreover, the space is not in proportion to the 

 axial canal in the stem, which in both genera is small and 

 circular. The space in these species is large enough to have con- 

 tained, in addition to the axial canal, such small plates as De 

 Loriol figured in Millericrinus Orbigny, and these, if present, 

 would talie the same position as the underbasals in that species. 



In all dicyclic Crinoids, the column rests either exclusively 

 against the underbasals, or, when these are very small, also partly 

 against the basals. The latter is the case in the two species of 

 Millericrinus where underbasals are known to be present. In 

 these species they form together with the basals a deep concavity 

 for the reception of the top stem joint, which occupies the whole 

 concavity, as beautifully shown by De Loriol in Mill, polydactylus 

 (PI. 110, fig. 1 a). In other species of Millericrinus in which 

 no underbasals have been observed, and in the genus ApioctHnus, 

 the structure is fundamentally the same, except that the columnar 

 concavity is formed exclusively by the basals, the underbasals 



