1890.] Genesis of the Actinocrinide. 251 
placed upon this structure in classification than it probably de- 
serves, as will be referred to later. 
Dorycrinus is directly traceable to a certain group of Devonian 
crinoids for which the name Gennzocrinus has been proposed. 
The latter genus embraces a few small forms, mostly from the 
Hamilton rocks. The species of Gennzocrinus, as for éxample 
G. cassedayi Lyon, are connected with Burlington and later 
Dorycrinus by such forms as lately have been found in the 
- Kinderhook beds of Central Iowa, and which have been described 
by Wachsmuth and Springer as D. immaturus and D. parvibasis. 
Dorycrinus, in combining the features of both, unites closely the 
Batocrinoid and Agaricocrinoid groups. It agrees with the first 
in the peculiar construction of the posterior side, in the simple 
anal opening, and in the radial grouping of the arms; with the 
second in the shape and structure of the calyx, and in the some- 
what flattened distal portions of the arms, in this respect approach- 
ing certain Eretmocrini. In the earlier, more generalized forms 
the close resemblance of Dorycrinus, Agaricocrinus and Eretmo- 
crinus or Batocrinus is far more striking than with later varieties 
which have become so greatly differentiated. The most prom- 
inent features, perhaps, to be noted in this connection are the 
monstrous ventral spines, often reaching a length of three to five 
inches, as in D. mississippiensis Roemer, and D. roemeri M. an 
W.; the immense basal expansion, as shown by D. missvuriensis 
(Shumard) and D. cornigerus (Hall); and the stout, heavy stalks 
with large, conspicuous nodal joints. 
Eretmocrinus differs from its nearest related genus—Batocrinus 
—of which it is manifestly an offshoot, chiefly in having long; 
flattened, lanceolate arms, a somewhat different ventral structure, 
and usually a more or less well defined lateral extension of the 
basals. The genus was rather short-lived, appearing in the Bur- 
lington and becoming extinct before the close of the Keokuk. 
Batocrinus is one of the most characteristic and widely spread 
forms of the family occurring in the lower Carboniferous. Its 
relations to the other genera have already been considered else- 
where and need not be repeated here. 
