Crinoidea, Pentacrininae 
35 
the bottom of the V, and not far removed from the syzygial face, a minute lumen. 
Just above this is the fulcral ridge, which consists of two ledges, One running about 
half-way up each slope of the V, at whose apex they may or may not meet. 
Th shape of the facet is more easily understood by considering that of 
cirral 1. This is somewhat like a short cone flattened on one side The base of 
the cone is the joint-face for cirral 2 ; the flattened side abuts on the hypozygal 
the rounded side has a groove for the fulcral ridge of the facet to work in ; above 
this comes the lumen, and then the cone slopes more rapidly to its apex. The distal 
joint-face (fig. 50) is transversely elliptical in outline, but bent transversely (i. e. 
cylindro-concave along the short axis); it also has a raised margin, and a short, 
stout fulcral ridge, below which as a rule is the lumen. The distal joint-face of 
cirral 2 (fig. 49) differs only in the accentuation of the marginal rim and of the 
ridge, and in the translation of the lumen to the centre of the fulcral ridge, which 
may be interrupted or continuous ; the ridge and lumen are markedly supracentral. 
Details vary, but the ellipse, the rim, and the short stout ridge are constant. 
A cirrus-facet approaching the triangulär indentation just described was men- 
tioned as occurring in one of the paratypes of I. tyrolensis (p. 32). Conversely in a 
few specimens of var. rnajor, the facet has a more oval outline (fig. 48), and 
resembles the facet in the holotype of I. tyrolensis (pl. II, fig. 37). In such cases 
the whole facet is enclosed by the epizygal; but there is still an impression on 
the hypozygal, due to the raising of the epizygal joint-face in the regions of the cirri. 
In all cases the proximal portions of the cirri have a slight downward direction. 
The peculiar shape of the facet and its deep burial in the nodal render it 
more convenient to measure the outer joint-face of cirral 1 ; and this serves for 
comparison with the measurements of the actual facet in other species. 
Diameter of stem . . . 
... 2-4 
4’2 
4-3 
4-3 
4-4 
mm. 
Width of side..... 
. . . 1 '5 
2-8 
27 
2-8 
2-6 
mm. 
Width of facet of cirral 1 
. . . 0-6 
0-8 
0-8 
0-8 
0-9 
mm. 
Height of facet of cirral 1 
. . . 0-5 
07 
07 
07 
07 
mm. 
Length of cirral 2 . . . 
? 
? 
0-2 
0-3 
p 
mm. 
Relations of the Subspecies to the type of the Species. — 
These have been partly discussed in connection with the height of the columnars. 
It will have been seen that, though the most tangible differences are those of mere size, 
yet, so far as the limited material permits any conclusion to be drawn, the direction 
of Variation is different in the two forms. Thus, while 1. tyrolensis normally has 
side-faces convex interradially and concave radially, major normally has straight side- 
faces; while I. tyrolensis normally has an elliptical cirrus-facet, major has a trian¬ 
gulär indentation; and while 1. tyrolensis normally has internodals of equal height, 
those of major usually vary according to their position in the internode. Although no 
accepted definition of a species would justify the specific Separation of these two 
forms. yet the facts cause one to regard them either as distinct local races or as 
the one a mutation from the other. On the latter hypothesis I. tyrolensis, with its 
less specialised cirrus-facet, would naturally be regarded as the earlier in time; 
and since the later date of major is confirmed by external evidence, the view 
that this form is a mutation seems worthy of adoption. For this reason I have 
refrained from speaking of it as a «variety». 
3 * 
