THE STEM AND ( ALY.V 19 



scries of basal pieces in I'nitrcmitcs, as in Pot6riocrinU8. This assumption would 

 have led him into error, but not into one of such a serious nature as he committed 

 in describing Pentremites as having only three radial pieces, two large ami one small, 

 the latter, be it remembered, being strictly interradial in position. No notice seems 

 to have been taken of Lyon's observations till 1869, when Billings published a 

 confirmation of them '. lie proposed to call the upper set of plates " subradials," 

 retaining the name " radials " for the fork-pieces. Meek and Worthen- pointed 

 out that the correspondence in position of the two rows of plates is an objection 

 to homologizing them with the basals and subradials of Crinoids which alternate witli 

 one another. Regarding the plates of the upper row or subradials (Billings) as the 

 true basals, they spoke of the lower series as the supplemental basals. Lyon had 

 described them in Cadaster alternatus as well as in Pentremites, ami Meek and 

 Worthen noted their presence in adult specimens of Orophocrinus stelliformis ; while 

 they went on to say that " although adult specimens of the type of the genus under 

 consideration have these lower pieces so solid as we see them in the true Pentremites, 

 young individuals show clearly that they are actually composed of Jive or six of the 

 upper joints of the column, enlarged and anchylosed together." They believed that 

 in one specimen of 0. stelliformis, which formerly belonged to Mr. "Wachsmuth, the 

 uppermost part of the stem is divided by longitudinal sutures corresponding with the 

 interbasal sutures, as is the case in liarycrinus. Wachsmuth 3 admits that " the 

 longitudinal sutures are not shown distinctly, but probably do exist in the specimen." 

 He objects, however, to the origin assigned by Meek and Worthen to the supple- 

 mental basals of Oropliocrinus, on the ground that no transition forms have ever 

 been found in this or in any allied species. But he goes on to say that he has some- 

 times noticed " a slight angular depression around the lower end of the cup. This 

 depression, which has somewhat the appearance of a suture, is caused by the more 

 rapid spreading of the upper portion of the basals. Such, at least, is the case in 

 some species of Codonites, Codaster, and Troostocrinus, in which the base appears as 

 if it might be dicyclic, but actually is monocyclic, and in which the lower part is 

 almost cylindrical, and resembles an elongate columnar joint, while the upper part 

 is conical." 



In all the three types mentioned by Wachsmuth there is a more or less elongated 

 base (PL XII. figs. 2, 3, 11 ; PI. XIII. figs. 3, 10, 12, 15 ; PI. XIV. fig. 17 ; PL XV. 

 figs. 1, 3 ; PL XVI. figs. 5, 7) ; and we think that he is probably correct in explaining 

 the occurrence of this furrow by the rapid increase in the width of the cup during 

 the later stages of its growth. This is certainly the explanation of the apparently 



1 American Journ. Sci. 1869, vol. xlviii. p. 83, and 1870, vol. 1. p. 220 ; Ann. & Mag. Nat. Hist. 1^7". 

 vol. v. p. 266, and 1871, vol. vii. p. 143. 



2 Report Geol. Survey Illinois, 1873, vol. v. p. 464. 



3 Proe. Davenport Acad. Nat. Sci. 1885, vol. iv. p. 79. 



d2 



