144 PROCEEDINGS OF THE ACADEMY OP [1886. 



1881. D. erraticus S. A. Miller, Joum. Cincin. Soc. Nat. Hist. (December), 1881. 

 Hudson River group. Cincinnati, Ohio. 



1880. D. navigiolum S. A. Miller, Joum. Cincin. Soc. Nat. Hist. (October), p. 4, 

 PI. 7, figs. 5, 6 a. Utica slate. Cincinnati, Ohio. 



1883. D. retractilis Walcott, 35th Rep. N. Y. St. Mas. Nat. Hist. (Extr. p. 5), PI. 

 17, fig. 4. Trenton limest. Trenton Falls, N. Y. 



HOMOCRINUS Hall, Rev. I, p. 77. 



This genus has been lately so often confounded with Poterio- 

 crinus, that for better information, we point out their distinctive 

 characters. Homocrinus differs from Poteriocrinus in the more 

 slender form of the calyx, in having no plates of the ventral tube 

 within the line of the first radials, in being provided with horse- 

 shoe-shaped articular facets, pierced by a round dorsal canal, and 

 in having at least three brachials. Contraiy to Poteriocrinus^ 

 the arms are not pinnulated, and they are composed of quadran- 

 gular joints with parallel lines of union. Its relations are much 

 closer with Parisocrinus^ which, however, has no separate dorsal 

 canal, and the first plate of the tube rests within the calyx. 



We add the following species : 



*1879. Homocrinus ancilla (Hall), Dendrocrinus ancilla, Trans. Albany Inst., vol. 

 X (Abstr. p. 9); also 11th Geol. Rep. Indiana by Collett, p. 271, PI. 15, fig. 

 19. Niagara gr. Waldron, Indiana. 



*1858. H. curtus (Miiller), Poteriocrinus curtus, Verb. d. naturh. Verein f. Rhein- 

 lande xii, p. 80, PI. 10, figs. 2-3 ; also Neue Echinod. Eifl. Kalk., p. 230, PI. 

 2, fig. 3. Schultze, 1866, Echin. Eifl. Kalk., p. 46, PI. 5. W. and Sp., 

 Parisocrinus curtus, Rev. 1, p. 115. Devonian. Eifel, Germany. 



*1882. H. davisanus (S. A. Miller), Poteriocrinus davisanus, Journ. Cincin. Soc. 

 Nat. Hist., p. 226, PI. 9, figs. 4, 4 a-b. Upper Helderberg gr. Deputy, 

 Indiana. 



*1882. H. nettelrothanus (S. A. Miller), Peteriocrinus nettelrothanus, Journ. 

 Cincin. Soc. Nat. Hist., p. 227, PI. 9, figs. 5, 5 a. Upper Helderberg gr. 

 Deputy, Indiana. 



*1876. H. nucleus (Hall), Dendrocrinus nucleus, 1st Edit. 28th Rep. N. Y. St. Mus. 

 Nat. Hist. PI. 15, figs. 7-9. Cyathocrinus nucleus, 2d Edit, ibid., p. 136. 

 Niagara gr. AValdron, Indiana. The arrangement of the plates at the 

 azygous interradius are not like in Cyathocrinus as Hall suggested, but 

 exactly like in Homocrinus. 



*1863. H. polyxo (Hall), Cyathocrinus polyxo, New Sp. Foss. Niagara group, p. 5; 

 28th Rep. N. Y. St. Cab. Nat. Hist. 1st Edit., PI. 15, figs. 10-17. Ibid. 2d 

 Edit. p. 135; also W. and Sp., Rev. i, p. 87; 11th Rep. Indiana by Collett, 

 1882, p. 264, PI. 14, figs. 10-17. Niagara gr. Waldron, Indiana. 



