1890.] Genesis of the Actinocrinida. 247 
-~ amented. The anal interradius has three ossicles in the second 
tier, with many smaller pieces in the succeeding rows. 
Amphoracrinus, in the general construction of the calyx, closely 
approaches some forms of Agaricocrinus, but its arms are very 
different, resembling more those of the preceding group. There 
are also other important distinctions. The earliest Agaricocrinus 
appears in the Kinderhook. At the beginning of the Keokuk a 
curious differentiation in some of the forms took place, giving rise 
to Alloprosallocrinus, of which but a single species is as yet 
known. The genus first mentioned is characterized by the flat- 
tened or concave dorsal region of the calyx, the free arms being 
given off low down on the margin of the basal plane. The rays 
are somewhat separated, especially on the posterior side, where 
a vertical row of anal plates is very noticeable. Ventrally, the 
calyx is greatly protuberant, and sometimes inflated not unlike 
that in Amphoracrinus. 
_ Dorycrinus is the direct lineal successor of Gennzocrinus, from 
which it should, perhaps, not be separated generically. The anal 
structure links it closely with Agaricocrinus. It differs, however, 
in having the general arrangement of the calyx more like Bato- 
principally in the long, lanceolate arms and inflated ventral parts. 
But the gradations are very complete, and it is often difficult to 
separate the forms of the two groups. In Batocrinus, the long 
anal tube, like that of the typical form of the family, is very 
prominent. The arms are short ; the plates in the second tier of 
the anal interradius three in number, and the orals large and well 
defined. : 
Actinocrinus and the genera following have only two pieces in 
the second anal tier. In the leading genus two rather well- 
defined sections are recognized: one with the arms equi-distant 
around the margin of the calyx; the others with the arms in 
ot usters, i ing a ly quinquelobate . Te 
S oom org, strongly quinq symmetry 
