276 THE VOYAGE OF H.M.S. CHALLENGER. 



possibly on account of the clumsy nomenclature adopted by these authors. Eamsay, 

 Phillips, and Etheridge have used it in this country ; but the well known German 

 palaeontologist 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 Bourgueticrinus from Apiocrimis. 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 Extracrinus, 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 

 diflPers 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 Extracrinus, however, are very different from those of Pentacrimis. 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 (PI. XIII. figs. 2-6, 9-11 ; PL XXII. 

 figs. 13, 14, 22; PI. 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 ; Pis. 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, instead 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 

 stria3 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 joint. These characters are well shown in several of the figures published 



1 Encrmiden, p. 270. 



