io8 
SMITHSONIAN INSTITUTION 
stout, reaching the full height of the crown ; it consists of 4 very long brachials 
beyond the short primibrach, tapering to a narrow end ; 1. ant. inferradial quad- 
rilateral, fairly wide. IBr of lateral arms 2. L. post, arm dividing on second 
primibrach into two rami, the inner one bearing a long branch on the second 
Alphabrach, and bifurcating on the second Betabrach into two equal branches ; 
the outer ramus divides in a similar way, but begins on the first Alphabrach. 
Thus there are only 6 branches on that side, in contrast to the 12 to 18 ramules 
of other species, and these are rather of the dichotomous type than the heteroto- 
mous. The arm arrangement on the anterior side is different; the anterior arm 
divides into two large apparently unbranched rami, and the r. ant. arm, decid- 
edly smaller than the former, has an unbranched inner ramus, while the outer 
branch, next to the anal series, divides again into slender finials scarcely more 
than half the length of the other arms. Brachials on both sides long and slender, 
similar to those of the median arm. Anal series strongly rounded, to the left 
of stem. Stem stout, asymmetric in position, with fairly long columnals, about 
1.2 mm. beyond the curve. 
The species is founded upon a single specimen, associated with the first two preceding ; 
it is a complete crown, exposed on both sides, and having a short section of stem attached. 
It may be regarded as an intermediate stage between Forms A and B, the latter being dis- 
tinctly foreshadowed in the arm arrangement, while it wholly lacks the ramule-bearing feature 
of the former. Yet the presence of the fourth arm, and the asymmetric position of the stem, 
determine its close relation to the Ordovician type, beyond question, thus furnishing another 
unmistakable link in the chain of evolutionary modifications so conspicuous in the history of 
this family. 
Horizon and locality. Eucalyptocrinus zone of Beech River formation, Brownsport 
group, Niagaran ; near Tuck’s Mill, Decatur County, Tennessee. 
Cremacrinus articulosus (Billings) 
Plate 2S, figs, p-ig 
Heterocrlnus articulosus Billings, Geol. Snrv. Canada, Dec. 4, 1859, p. 51, pi. 4, fig. 8 . — Castocrinus 
articulosus Ringueberg, Ann. New York Acad. Sci., 4, 1889, p. 395, pi. 10, fig. 4. — .Springer, A Tren- 
ton Echinoderm Fauna, Mem. 15-P, Geol. Surv. Canada, 1911, p. 25. 
I am illustrating this species rather fully chiefly to show the incipient 
dwarfing of the r. ant. arm in the Ordovician stage of the g'enus. It has been 
known heretofore only from very scant material, consisting solely of the im- 
perfect type specimen from Ottawa, Canada, which was refigured by Ringue- 
berg. The single arm preserved shows very clearly the strongly nodose axil- 
laries which constitute its leading character. Our knowledge of this rare form 
has been enlarged in recent years by the acquisition of a fine series of specimens 
from Kirkfield, in Ontario, in exquisite preservation, by which all the charac- 
ters are brought out in detail. These are supplemented by an excellent specimen 
from an equivalent horizon in Kentucky. By a selection from this material the 
heterotomous structure of the two equal rami of the lateral arms, with their 
