276 THE VOYAGE OF H.M.S. CHALLENGER. 
possibly on account of the clumsy nomenclature adopted by these authors. Ramsay, 
Phillips, and Etheridge have used it in this country; but the well known German 
paleontologist Quenstedt," who has probably seen it in greater abundance than any other 
naturalist, speaks of it in a decidedly scoffing tone. This, however, is only to be expected 
from one who does not separate Bowrgueticrinus from Apiocrinus. Zittel mentions 
Austin’s name, but without committing himself to an acceptance of it; and I have reason 
to believe that M. de Loriol is prepared to accept the genus after it has been redefined 
in a manner which is consistent with the present state of our knowledge. 
The genus Hxtracrinus, which includes the two groups “ Briariden” and “ Subangu- 
laren” of Quenstedt, is thus distinguished by the presence of under-basals (dorsocentral 
plate, Austin) and the downward prolongation and jointing of the radials. But it also 
differs very markedly from the Post-Liassic and recent Pentacrinites in the characters of 
its stem and arm-divisions. 
The precise structure of the stem of Extracrinus, i.e., the relations of its nodal and 
internodal joints, has yet to be worked out. Some fragments of stem, probably from 
near the top, seem to consist entirely of nodal joints; while in others there are several 
joints between any two whorls of cirri, just as in the ordinary Pentacrinites. The joint- 
faces of Eaxtracrinus, however, are very different from those of Pentacrinus. In the 
latter genus, the five petaloid figures indicating the position of the stem ligaments are 
more or less oval in shape, pointed at one or both ends, and bounded by strong ridge- 
like processes, with alternating furrows (Pl. XIII figs. 2-6, 9-11; Pl. XXII. 
figs. 18, 14, 22; Pl XXX. figs, 25-30; Pl XXXa. fig. 7; Pl. XXXII. fig. 3; 
Pl. XXXVII. fig.22). There may be only about three of these on each side of the 
petal, as in most recent forms, or there may be from six to twelve of a smaller size. 
But all of these ridges, except those most centrally placed, slant inwards from the edge 
of the joint, where their outer ends cause the denticulation which is so marked in all but 
the oldest specimens (Pl. XIX. figs. 2-5; Pl XXVII. fig. 1; PL XXXa. fig. 6; 
Pl. XXXI. fig. 3; Pls. XXXV., XXXVL). 
In Extracrinus, however, the five interradial petals are quite narrow, and much less 
distinctly oval than in Pentacrinus, sometimes being linear with rounded outer ends. 
Even when the joints are stellate the petals do not occupy more than the central portion 
of each ray of the star, stead of the whole of it as in Pentacrinus; and when the joints 
are pentagonal or circular there is a more or less triangular space between every two 
petals, which is plain and devoid of sculpture. Then again the markings at the sides of 
the petals are much more delicate than in Pentacrinus, having more the character of 
strize or crenulation than of coarse ridges. They are also much more numerous than in 
Pentacrinus, and are strictly limited to the sides of the petals, not reaching the outer 
edge of the jomt. These characters are well shown in several of the figures published 
1 Encriniden, p. 270. 
re re 
