1886.] NATURAL SCIENCES OF PHILADELPHIA. 221 



form, and that the plate actually rests against the outer faces of 

 the basals, and not between the hasals as in the case of the inner 

 plate in Stemmatocrinus and Cupressocriyius, which Carpenter 

 (Chall. Rep., p. 152), as we think, erroneously took to be a stem 

 joint. The plate in Apiocrinus niagnificus is not, as should be 

 supposed from appearances, disposed radially, but interradiall}', 

 as shown by comparison with species having a pentangular stem. 

 It attained its radial angles accidentall}^ by adapting its form to 

 the basal concavity which is naturally angular. The case is parallel 

 to that of Eucalyjytocrinus and Bari^andeocrinus, in which the 

 angles of the upper column are shaped so as to conform with 

 surrounding plates, which are in that genus the radials. 



In Apiocrinus Parkinsoni (Pts. 27 and 28) and in A. roissyanus 

 (Pts. 41-45), the basal structure is similar to that of Ichthyocrinus, 

 but, while in the latter the underbasals are persistent through 

 life, they may have disappeared in the other. The basal concavity is 

 shallow, and in both species the upper portions of the column taper 

 abruptlj'^ in a downward direction. The same is the case fre- 

 quently among the Ichthyocrinida3. 



The base of Guettardicrinus and Rhizocrinus is in a similar 

 condition, but less concave. For Rhizocrinus we refer to the 

 Challenger Report, PI. x, figs. 5 and 9. The top stem joint 

 resembles closely that of Ajnocrinus, and also the basal con- 

 cavity, which also here is filled completely by the top joint. The 

 columnar canal is circular or ovoid, and much smaller than the 

 pentangular space within the basal ring, which, contrary to mono- 

 C3^clic Crinoids, is directed radially. The same is the case in 

 Guettardicrinus. Both genera are built on the same plan as 

 Apiocrinus, and if the latter possessed underbasals, these plates 

 were also present in Rhizocrinus and Guettardicrinus. 



In the Pentracrinidffi, and not only in Extracrinus, in which 

 underbasals have been observed, but also in Pentracrinus and 

 Metacrinus in which they are said to be absent, the angles of 

 the column, without exception, are interradial, the lateral cirrhi 

 radial, but, while the axial canals of Metacrinus, and probably 

 Extracrinus, are radial ^ in conformity with dicyclic Palseocri- 

 noids, they are interradial in Pentacrinus,^ as in all monoc}'"- 



1 Challenger Report, PI. 12, figs. 1 and 2, and PI. 41, figs. 6 and 7. 



2 PI. 12, figs. 15 and 16 ; PI. 20, figs. 1 and 2 ; PI. 22, figs. 1, 2, 7 ; PI. 23, 

 figs. 1 and 2 ; Pi. 26, fig. 11 ; PI. 27, figs. 2, 3 ; PI. 30, fig. 4 ; PI. 34, figs. 8 

 and 9 ; PI. 37, figs. 14 and 15. 



