MORPHOLOGY 41 



in the calyx of the Flexibilia. Striking examples of this character may be seen 

 in numerous figures under the following genera, viz. : Forbesiocrinus, Plates 

 XXIII, XXV-XXIX; Eutaxocrinus, Plate XLVIII; Taxocrinus, Plates LII, 

 LIII, LV, LVII-LX, LXII ;Onychocrinus, Plates LXVI, LXVII, LXIX, LXX. 

 The form and construction of the posterior basal furnishes the chief 

 ground for differentiation between Forbesiocrinus and Taxocrinus and the 

 families which they represent, being suturally connected at the distal end with 

 other plates in the former, and only with perisome in the latter. 



c. Radials and Brachials 



The radials in the Flexibilia are subject to considerable modification, ex- 

 hibiting wide contrast in form and proportions. They are most prominent in 

 the Lecanocrinidae, in which they are usually the largest, and in typical forms 

 by far the largest plates in the calyx (Pis. I-XV). This disproportion is great- 

 est in Pycnosaccus and Nipterocrinus, in which the great size of the radials, 

 coupled with the extreme smallness of the succeeding brachials, produces a 

 f acies more like that of the Inadunata than of the Flexibilia ; in fact it was not 

 until I obtained the proof that the rays in these genera are connected by 

 perisome that their relationship to the latter group became clear (Pis. XI, 

 fig. gc; XII, figs. 2a, b, 3a, b; XV, fig. 10b). 



In the Ichthyocrinidae the relative proportions of the plates are exactly 

 reversed, the radials being smaller than the succeeding brachials, so that the 

 ray widens upward like a fan (Pis. XXXII, XXXIX, XLIV). In some species 

 of Ichthyocrinus, and in Cleistocrinus and Amphicrinus , the radials are partly 

 or wholly buried under the column; and in Calpiocrinus they are sometimes 

 overgrown by the inf rabasals. In the Sagenocrinidae and Taxocrinidae there 

 is no very marked difference between the radials and the lower brachials, the. 

 rays being of approximately uniform width. There are occasional exceptions 

 to these rules, as for example Lecanocrinus bacchns (PI. II, figs. 27, 28a), in 

 which the ray looks much like that of Ichtliyocrinus; but in general they fur- 

 nish a useful guide for the reference of a specimen to its proper family. In 

 Parichthyocrinus, which is an intermediate type between the Ichthyocrinidae 

 and Taxocrinidae, the right posterior radial alone is greatly reduced in size by 

 encroachment of the posterior basal, and the primibrach following it is some- 

 times correspondingly 'enlarged to a greater size than its fellows (PI. LXI, 

 figs. 11, 12, 14). 



Compound radials are unknown in this group, except in the right pos- 

 terior ray of those genera having a radianal in the primitive position. 



The primary brachials vary in number from one to three or more, the 

 preponderating types being those with 2, or with 3, primibrachs ; while the 

 others are exceptional, save in Onychocrinus where more than three is a 



