ii6 
SMITHSONIAN INSTITUTION 
posed. Thus while a species with the main arms partly exposed might belong to either genus, 
we can be fairly certain that one in which these parts are hidden by the outer ramules does 
not belong to Halysiocriiius. 
Coincident with the development of the axil-arm system and the enlargement of the 
simple radials came the separation of the two segments of the 1. ant. compound radial. This, 
as before shown, was a progressive feature, apj^earing first in the Silurian among species of 
this genus pari passu- with the axil-arms, and becoming established as an invariable structure 
in the later stages of the family. It is a thorouglily reliable character for distinguishing the 
two genera here defined from those preceding them, as is also the fusion of the two left basals 
into one triangular or convex plate not connected with the stem, this being especially valu- 
able because determinable from the base alone. The minor differences by which the two are 
separated are not conspicuous, but the division, confirmed as it is by stratigraphic considera- 
tions, is useful, and the characters if carefully observed are usually sufficient for identifying 
them. In some of the Gotland species the fused left basal is almost, and rarely quite, as wide 
as the hinge. 
Calceocrinus foerstei netv species 
Plate 29, figs, pa, b, 8a, b, p, 10, ii 
Crown of medium size, ranging from 37 to 50 mm. in height, and fairly 
stout. Cup as seen from 1. ant, side relatively short, obtusely trapezoidal, but 
little constricted; height to the width at hinge as i to 1.4. Median ( 1 . ant.) arm 
very stout, simple, and longer than the axil- arms ; brachials averaging 3.4 mm. 
high by 4 mm. wide in a large specimen; segments of 1 . ant. R connected, infer- 
radial elongate quadrilateral. Lateral IBr 2. Main-axils of lateral arms 5 to 8. 
Axil-arms stout, with brachials of exposed ramules as wide as high, about 2.5 
mm. in large specimen; outer (adanal) ramules following Betabrachs closely 
apposed, decreasing regularly in size stemwards, and forming the chief visible 
arm-branches ; when closed they hide from view the main arms, as well as the 
inner (abanal) ramules. Anal tube stout, composed of large segments resem- 
bling brachials, projecting beyond the axil-arms; anal x large, strongly rounded, 
may be slightly indented by pressure of column; subanal piece fairly large, wider 
than high, usually more or less indented. Stem stout, apparently rather short, 
the longest one preserved beginning to taper at 5.5 cm.; columnals about 1.5 
mm. high and 3 mm. wide in middle portion ; with but little curvature, the stem 
lying closely parallel to the anal series. 
This species is described upon the evidence of eight crowns, mostly well preserved, and 
one having the short stem probably to near the distal end ; three of them are figured. In the 
exceptional presence of a quadrangular inferradial and the resulting connection of the segments 
of 1. ant. R., it shares with the Silurian species of Cremacrinus in the survival of this primitive 
Ordovician structure, and in this character differs from all other species of this genus except 
C. pinnulatus and ivterpres of Gotland. In the approximation of the outer ramules of the 
axil-arms it is of the type of the Gotlandian C. tcnax. One specimen, figure 10 , somewhat 
distorted, differs from the others in the proportions of the brachials and axil-arms, but upon 
the more essential characters appears to belong with the species. It was figured under the 
impression that it might have to be separated. Figure 1 1 is from a set of arms of unusual size 
which exhibits especially well the characteristic disposition of the axil-arm in the extreme 
stage. 
