nAAl 504 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
| 
its culmination in the Upper Burlington limestone and Keokuk group, where 
| l it became extinct, being the last survivor of the family. In Europe it is 
1) i represented at Tourney, Belgium, in the Yorkshire regions of England, and 
tl : } | at Waterford, Ireland; but no trace of it has been found in the higher Car- 
} i | | | boniferous rocks of Scotland or Russia. 
| ia Remarks. —The genus Actinocrinus was made by the earlier writers on 
h |. j | | Crinoids a receptacle for all—or nearly all— Camerata with a monocyclic 
meh base, and in which an anal plate was introduced within the radial ring. This 
| HI | accounts for the fact that the number of species referred to it reaches nearly 
| | three hundred. The first departure from this rule was made by Austin in 
ie 1843, who introduced the genera Amphoracrinus and Periechocrinus ; and | | 
| ia although his descriptions were meagre and partly incorrect, he gave well 
| | known types for both forms, so that they could be readily identified. Owen | 
4 | ~ and Shumard followed in 1852 with Megistocrinus, and F. Roemer in 1854 | 
, | : | | | with Dorycrinus. In the same year Casseday proposed the genus Batocrinus, | 
: i | . | and in 1859, in company with Lyon, Hretmocrinus. But all these genera, 
i | | | with the exception of Megistocrinus, were ignored by Hall, who from 1859 
/ ai || | to 1861 described a great number of new species of this group. A more 
j important step toward a better understanding of this group was taken by 
| Meek and Worthen, who not only accepted the genera theretofore proposed, 
(he NU but introduced three new ones, viz., Steganocrinus and Strotocrinus in 1866, 
i) i | | and Physetocrinus in 1869, which also are now generally accepted. After- | 
Vane | wards we proposed the genera Gennwocrinus and Teleiocrinus, and in 1881 the 
| ie fall | number of species retained under Actinocrinus, after deducting numerous 
Hl : synonyms, was reduced to less than fifty. But even these species were 
Vig ual susceptible of division into two sections, as already pointed out in 1866 by 
A | ae Meek and Worthen, viz., 
Hf YI 
hl 
| 
1} A — species in which the higher brachials, sometimes from the second costals up, are | 
" my | grouped together, so as to form five protuberant lobes, from which the arms are 
an | given off from alternate sides. : 
iN B— species in which the arm bases are arranged. in a continuous series around the calyx, | 
| an 
( Bill | i. é., the interbrachials are separated from the interambulacrals by the arm-bearing 
1 . brachials. 
These differences we regard as amply sufficient for generic separation. 
|. In addition to them there is a constant difference in the number of brachials 
al | beyond the costals, — the higher orders of brachials in all species of section 
Ni | A consisting of two or three plates, while each such order in those of sec- 
