66 THE VOYAGE OF H.M.S. CHALLENGER. 
plates on the arms of Gissocrinus, which he described in his generic diagnosis’ as 
“pinnulee brevissimee verruceeformes.” They do not correspond to the “assule ambula- 
crales” of Gissocrinus; for these, as pointed out by Wachsmuth and Springer,” are the 
joints of the arm-bases which are recumbent upon the vault, being raised above the 
general level, and “covered by small alternating plates like the free arms.” 
Thus, then, the expression “ pinnule” was used by Angelin for three different types of 
structure in Habrocrinus, Crotalocrinus, and Gissocrinus respectively. The first of these 
represent the true pinnules of recent Crinoids; while, as was first recognised by Zittel,’ 
the plates on the arms of Gissocrinus represent the “ Saumplittchen” which Miiller had 
described on the ambulacra of Pentacrinus. He takes the same view of the plates which 
Angelin called “rudimenta pinnularum semiglobosa” in Cyathocrinus ramosus. The 
corresponding plates in Cyathocrinus longimanus have indistinct cross markings; and 
Messrs. Wachsmuth and Springer have interpreted this as indicative of segmentation into 
pinnule-joints ;* for they speak positively of ‘‘ two rows of five successive plates each, one 
row being given off from the right, the other from the left side of the furrow, and perfectly 
covering it.” The arms of Cyathocrinus, however, are only single-jointed ; and they 
state elsewhere’® that “in double-jointed arms every joint at each side bears a pinnule, 
while in those with single joints the pinnules are found only on alternate sides.” But 
Angelin’s figures show that on five arm-joints there are twelve of these rudimentary 
pinnules, six on each side, while in Gissocrinus there are from four to six on each arm- 
joint. In spite of these facts, however, Wachsmuth and Springer give it as their opinion 
that these plates which cover in the ambulacral groove in the arms are the homologues of 
the pinnules, though too rudimentary to be ranked as such.® [See p. 84. | 
The chief point of their position (and they make the most of it) is the apparent 
segmentation of the “rudimentary pinnules” into five joints, as shown in Angelin’s 
figures of Cyathocrinus longimanus. It would be very desirable if this could be verified 
on the actual specimens. The presence of two rows on each side of the ambulacrum in 
Cyathocrinus, Gissocrinus, &c., is nothing unusual ; for they represent the side plates and 
covering plates of Neocrinoids, of which there may be from five to seven to one arm-joint. 
Precisely similar plates occur on the pinnules as well as on the arms ; and they also form 
part of the skeleton round the radiating tubes beneath the vault of Actinoerimus “ which 
connect with the ambulacral furrows in the arms.”7 But I think that Wachsmuth and 
Springer would hesitate before considering the two upper rows of plates in these radiating 
tubes as ‘rudimentary pinnule.” 
1 Tconographia Crinoideorum, p. 10. * Revision, part ii. p. 91. 3 Paleontologie, pp. 338, 354. 
* Revision, part 1. pp. 24, 82. 5 Id., part ii. p. 24. ® Thid., part i. p. 82. 7 Thid., part ii. p. 28. 
