REPORT ON THE CRINOIDEA. 277 
by different paleontologists, e.g., on pl. 53 of Buckland’s Geology and Mineralogy, 
figs. 9-13; on Tab. 101 of Quenstedt’s Encriniden, especially figs. 24, 27, 33, and 37; 
and also on pl. 12 of the Messrs. Austin’s Monograph, figs, d,f, k,n, 0, 7. None of these 
authors, however, seem to have noticed the distinction of this type of joint from that of 
the ordinary Pentacrinide, either recent or fossil ; and attention was first drawn to it by 
de Loriol, as will be pointed out subsequently. 
In the ordinary Pentacrinide, as in the multiradiate Comatule, there is no special 
regularity in the mode of division of the secondary and tertiary arms. The twenty 
secondary arms borne upon the distichal axillaries may either remain simple, or fork 
again, once or oftener. But in most cases the forking is very irregular. Secondary 
(palmar) axillaries may appear upon any of the four secondary arms; and the two 
tertiary arms borne by them are of equal size, and have equal power of forking again, 
though as a rule they do not all do so. A good instance of this is shown in Miller’s 
figure 1 of Pentacrinus asterius (caput-Meduse), which is represented more diagrammati- 
cally in Quenstedt’s Tab. 97, fig. 3. A similar arrangement has been described by 
Liitken in Pentacrinus miilleri2 while it also occurs in Pentacrinus maclearanus, 
Pentacrinus wyville-thomsoni, and Pentacrinus alternicirrus (Pl. XIV.; Pl. XV. fig. 1; 
Pl, XIX. fig. 2; Pl. XXV.; Pl. XXVI. fig. 4). In all these cases the secondary (and 
tertiary) axillaries are limited to the outer arms of each successive pair, so that the arrange- 
ment of the arms on the ray is 2,1; 1, 2; or 2, 1,1; 1,1, 2.? But the two (or four) 
inner arms are equivalent to the outer ones in all respects, neither of them dividing again. 
While the arm-division in Hatracrinus proceeds to a much greater extent than in 
Pentacrinus, it is confined as a rule to the sides of the ray, only the outer arm of each 
successive pair bearing axillaries, just as in the secondary and tertiary arms of 
Pentacrinus asterius, Pentacrinus miilleri, &e. The four tertiary arms which spring 
from each pair of palmar axillaries are rarely of equal size, and never absolutely equi- 
valent. The two inner ones are usually rather the smaller, and except in some forms of 
Extracrinus subangularis do not divide again. Each of the larger outer arms, however, 
divides again after a few joints, but the division is unequal. The smaller inner face of 
the axillary, 7.e., that turned towards the other axillary, bears a slender armlet; while the 
main arm-trunk is continued directly onwards without change of direction. It gradually 
diminishes in size, and gives off at short intervals a series of slender armlets from its 
inner side, but it never really forks. But for the pinnules borne by it and its 
subordinate armlets, one would be almost inclined to say that the distichal axillary bears 
two secondary arms which have long slender pinnules placed at intervals upon their 
adjacent inner faces, but none whatever upon their outer sides. These organs are real 
1 Op. cit., p. 48, pl. i. 2 Om Vestindiens Pentacriner, loc. cit., pp. 2038, 204. 
3 The Caribbean Antedon spinifera often shows exactly the reverse condition to this. Palmar axillaries are frequently 
only developed on the inner pair of the four secondary arms, so that the grouping on each ray is 1, 2; 2, 1. 
