1890.] Genesis of the Actinocrinide. 249 
becomes greatly intensified. In the earlier species the free arms 
are slender, growing much stouter in the Burlington and Keokuk, 
and in the latter often also branching one or more times.. This 
development is accompanied by an increasing massiveness of the 
calyx plates and a change of the simple convexity of the ossicles 
into great, rude nodosities. Another marked feature is the ten- 
dency for the rays to separate from one another above the second 
brachials, forming prominent radial extensions before giving off 
the freearms. At the same time the interradial areas become 
somewhat more depressed. The quinquelobate calyx is thus 
produced; the form upon which the genus was was founded. In 
general it may be said that the earlier forms were of small size, 
delicately constructed and ornamented, and that they gradually 
became very much larger and more massive, with a rough, 
rugged ornamentation. 
The more striking points in the development of the anatomical 
features in Actinocrinus, as here briefly traced, apply to the 
other genera here mentioned, and also to the members of other 
related families. Besides, Dorycrinus developed huge vertebral 
spines; Batocrinus, an immense disk-shaped calyx ; Eretmocri- 
nust broad lanceolate arms; Strotocrinus,a large rim stretching 
out laterally from above the tertiary brachials ; and Steganocrinus, 
monstrous radial extensions, from which the free arm sprung. 
Generic Relationships——As previously stated, Periechocrinus 
and Megistocrinus are closely related, but differ considerably 
from other members of the family. Their recorded history also 
extends over a much longer period than that of the other twelve 
genera. Periechocrinus occurs first in the Niagara,—large, thin 
plated forms, nearly devoid of ornamentation, and having tall 
obconic calyces, with long arms branching one or more times, 
The evidence of this type in the American Devonian is as yet 
rather meager, though in Europe abundant testimony of its ex- 
istence in rocks of similar age is not lacking. The forms found 
in the Lower Carboniferous present a somewhat different aspect 
from those of the earlier periods, having the calyx very much 
shortened and proportionately broadened*at the base of the free 
arms, besides differing in several other respects. 
