28 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
the proximal ring of the latter represents an independent element, and that 
their second ring of plates corresponds morphologically to the proximal one 
in monocyclic forms. This is now accepted by almost every writer. Another 
important contribution to the knowledge of Crinoids was made by a paper 
on A/lagecrinus,* a Carboniferous genus, in which the ventral surface is cov- 
ered completely by five oral plates, thus retaining persistently the structure- 
of the Azfedon larva. 
The progress in the knowledge of fossil Crinoids was paralleled by that 
among recent ones, of which a great number of new forms were obtained by 
the dredging expeditions. Until about 1860 we possessed of Stalked Cri- 
noids only a few specimens of Pentacrinus caput-meduse, and one or two of 
Lolopus Rawson’; but since then new discoveries followed in rapid succes- 
sion. In 1864, Sars described the genus Riizocrinus ; Jeflreys, in 1872, a 
new species of Pentacrinus from the Bay of Biscay ; de Pourtalés, in 1874, 
a second species of Rhizocrinus. The dredgings by the “Blake” under the 
supervision of A. Agassiz in the Gulf of Mexico brought to light the new 
Comatulid genus Afelecrinus, and a large number of specimens of Penta- 
crinus ; those of the “ Albatross” in 1891, off the Galapagos Islands, the 
remarkable genus Calamocrinus. The largest results, however, were obtained 
by the “Challenger” expedition, which produced three new genera of 
Stalked Crinoids, and one of Comatulz. Progress in morphology and em- 
bryology in later years has been as rapid as the discovery of new species ; 
in proof of which we need only refer to the works of Allman, Goette, Sars, 
Greeff, Ludwig, Pourtalés, Bell, Barrois, W. B. Carpenter, Wyville Thomson, 
Perrier, Bury, P. H. Carpenter, Vogt and Yung, and A. Agassiz. 
The oral question was finally solved in 1888 ft by our discovery of the 
remarkable specimen of Zaxocrinus, which proved conclusively that in forms 
with large plates around the oral centre, asymmetrically arranged, the orals 
are represented not by the central plate alone, as we had supposed, nor by 
the four large and two smaller proximals, as claimed by Dr. Carpenter, but 
by the so-called central plate together with the four large proximals; the 
disturbance in the arrangement of the plates being due to the introduction 
of anal plates. It was further proved that in specimens in which the whole 
* On Allagecrinus, the Representative of a new family, etc. By P. H. Carpenter and R. Etheridge, Jr. 
(Ann. and Mag. Nat. His., April, 1881, pp. 281-297). 
+ Discovery of the Ventral Structure of Taxocrinus and Haplocrinus, and Consequent Modifications in 
the Classification of the Crinoidea; by Charles Wachsmuth and Frank Springer (Proceed. Acad. Nat Sci. 
Phila., 1888, pp. 337-361). 
