REPORT ON THE CRINOIDEA. 65 
a lily of the Lilium Martagon type, in which each petal is curved upon itself, the 
pinnules of the arms spreading laterally more and more as the crown is more fully 
open. .. . When disturbed, the pimnules of the arms first contract, the arms straighten 
themselves out, and the whole gradually and slowly closes up.” ? 
Taking all these facts into consideration, I cannot but feel that a homology is of 
no real value when it is based upon the physiological condition of the arm-grooves in 
the dead animal, and still more in the fossil forms, closed up as they are in every 
possible way, especially when this condition is one which the living animal only assumes 
when disturbed, and cannot long maintain without the risk of being both starved and 
suffocated. The whole poimt of Wachsmuth and Springer’s argument, however, is 
based upon this closure of the arm-grooves by pinnules and covering plates respectively ; 
and they attempt to support the proposed homology by certain morphological considera- 
tions, which must now be discussed. 
On each side of the brachial ambulacra of Cyathocrinus iowensis there are, according 
to Wachsmuth,” two rows of minute alternating plates, six to each arm-joint. <A 
similar structure is shown in one of Angelin’s figures of an arm-fragment of Gissocrinus 
punctuosus, though in another figure only one row of plates is visible at the side of the 
ambulacrum instead of two, while the explanation of the figures simply says, “ Digiti 
cum pinnulis magnitudine aucta.” A somewhat different structure appears in Cyatho- 
erinus longimanus figured on the preceding plate.* In this species, according to 
Wachsmuth and Springer,’ “there are in place of only two, a series of five successive 
plates from each side, alternately arranged. The plates of each side taper toward the 
end and enfold over the furrow, covering it as perfectly and in the same manner as in 
the two former cases (7.e., Cyathocrinus iowensis and Gissocrinus punctuosus). Angelin 
gives no description, but in his table of contents he calls the successive plates ‘ pinnule.’” 
Although, however, Angelin may have used the word “ pinnule” for these lateral plates, 
I doubt how far he meant to imply any correspondence with the true pinnules of 
Actinocrinus and Platycrinus and other types in which they occur. For in his definition 
of Crotalocrinus he gives the same name to the lateral processes of the arms by which 
they are united into the well-known complex network ; and he then continues, “ Perisoma 
ventrale totum assulis variantibus tectum; assule ambulacrales minute, biseriate ab 
imis brachiis usque ad extremos digitos radiatim exeunt, quarumque numerus prout 
digitorum numerus magis magisque per repetitam dichotomiam increscit.”° The magni- 
ficent figure which he gives of the ventral surface of an expanded Crotalocrinus pulcher* 
shows that the minute ambulacral plates on the arms are identical with the covering 
1 Quoted by Pourtalés, On a New Species of Rhizocrinus from Barbadoes, Mem. Mus. Comp. Zoél., vol. iv., 
No. 8, p. 29. 
2 Amer. Journ. Set., vol. xiv. p. 121. 3 Tconographia Crinoideorum, Tab. xxvii. fig. 1f. 
4 Ibid., Tab. xxvi. figs. 4, 5. 5 Revision, part i. pp. 24, 25. 
7 Ibid. Tab. viii. fig. 6; see also Tab. xxv. figs. 15, 17 
6 Tconographia Crinoideorum, p. 26. 
li9 
(ZOOL. CHALL. EXP.—PART XXx1I.—1884.) 
