28 THE CEINOIDEA CAMEEATA 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 Allagecrinus^^ a Carboniferous genus, in which the ventral surface is cov- 

 ered completely by five oral plates, thus retaining persistently the structure 

 of the Antedon 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 o^ Pentacriniis caput-mediisw, and one or two of 

 Holopiis Raivsoni; but since then new discoveries followed in rapid succes- 

 sion. In 1864, Sars described the genus Rhkocriniis ; Jeffreys, in 1872, a 

 new species of Pentacrinus from the Bay of Biscay ; de Pour tales, in 1874, 

 a second species of Ehkocrimis. The dredgings by the "Blake" under the 

 supervision of A. Agassiz in the Gulf of Mexico brought to light the new 

 Comatulid genus Atelecrinus, and a large number of specimens of Fenta- 

 criniis ; those of the "Albatross" in 1891, off the Galapagos Islands, the 

 remarkable genus Calamocrimis. The largest results, however, were obtained 

 by the " Challenger " expedition, which produced three new genera of 

 Stalked Crinoids, and one of Comatulse. 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 w^orks of All man, Goette, Sars, 

 GreeflP, Ludwig, Pourtales, Bell, Barrois, W. B. Carpenter, Wyville Thomson, 

 Perrier, Bury, P. H. Carpenter, Yogt and Yung, and A. Agassiz. 



The oral question was finally solved in 1888 t by our discovery of the 

 remarkable specimen of Taxocrinus, 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. Etlieridge, Jr. 

 (Ann. and Mag. Nat. His., /Ipril, 1881, pp. 281-297). 



t Discovery of the Yentral 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). 



