REPORT ON THE CRINOIDEA. 65 



a lily of the Lilium Martagou 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 pinnules 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 point of AVachsmuth and Springer's argument, however, is 

 based upon this closure of the arm-grooves by pinnules and covering plates respectivel}- ; 

 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 Ci/athocrinus iowensis there are, accordiuo- 

 to Wachsmuth,'^ two rows of minute alternating plates, six to each arm-joint. A 

 similar structure is shown in one of Angelin's figiu'es of an arm-fragment of Gissocrinus 

 pimctuosus,^ 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, " Dioiti 

 cum pinnulis magnitudine aucta." A somewhat diff"erent structure appears in Cyatlio- 

 crinus longimanns 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 {i.e., Cyathocrinus ioioensis and Gissocrinus punctuosus). Angelin 

 gives no description, but in his tal)le of contents he calls the successive plates ' pinnulse.' " 

 Although, however, Angelin may haA^e used the word " pinnulje " 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 

 tliey are united into the well-known complex network ; and he then continues, " Perisoma 

 ventrale totum assulis variantibus tectum ; assulfe ambulacrales minutae, biseriatfe ali 

 imis brachiis usque ad extremes digitos radiatim exeunt, quarumque numerus prout 

 digitorum numerus magis magisque per repetitam dicbotomiam 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 l-iy Pourtales, On ,1 New Species of Rhixocrhnis from Barliadoes, Mem. Mus. Comp. ZoiiL, vol. iv., 

 No. 8, p. 29. 



2 Amcr. Journ. Sci., vol. xiv. p. 121. ^ Iconograpliia Crinoideoruni, Tab. xxvii. fig. 1/ 

 < Ibid., Tab. xxvi. figs. 4, 5. * Revision, part i. pp. 24, 25. 



8 Iconographia Crinoideonim, p. 26. ' J^'i''- Tali, ■i-iii. fig. 6 ; see also Tab. xxv. tigs. 15, 17. 



(ZOOL. CHALL. EXP. — PART XXXII. — 1884.) li 9 



