122 PROCEEDINGS OF THE ACADEMY OF [1886. 



Generic Diagnosis. General form pja-iform, more protuberant 

 upon the azygous side. Calj^x composed of five basals, four 

 large radials, and a large azygous plate. The latter with its left 

 side extending to the upper margins of the four large radials, its 

 sloping right side supporting the fifth radial, which is small and 

 triangular, and, taken jointly with the azygous piece as one plate, 

 the two resemble in form the four large radials, only that the 

 arm-facet is pushed to one side. 



Basals large, pentagonal, nearly equal in size. Four of the 

 radials pentagonal, the smaller one subtriangular, resting upon 

 the right sloping upper side of the azygous plate, which is 

 irregularly pentagonal. Arm-facets occupying scarcely one-third 

 of the width of the radials. Arms simple, without pinnules ; 

 composed of quadrangular joints, arranged parallel to each other. 

 Column cylindrical. 



The onl}^ known species is : 



1843. Hoplocrinus dipentas Leuchtenberg (Apiocrinus dipei.tas), Buschreibung 

 neuer Thierreste d. Urwelt von Zarskoje. Selo, yi. 17, Tab. ii, figs. 9-10; 

 also Eichwald, 1856, Bull, de Moscow, i, p. 115. Homocrinus dipentas, 

 1859, Eichwald, Leth. Ross., v, p. 583, Tab. 31, figs, a-c (excl. specimen 

 from Erras). Hybocrinus dipentas, 1864, Volborth, Bull. d. I'Acad. de. St. 

 Petersb., Tome viii, p. 178. Homocrinus dipentas, 1865, Eichw., Bull. d. 

 Moscow, No. ill, p. 159. Hybocrinus dipentas, 1S65, Volborth, Bull, de 

 Mosc, No. iv, p. 443. Homocrinus dipentas, 1866, Eichwald, Bull, de 

 Moscow, No. 1, pp. 149-161, Tab. 8, figs. 2, 3, 4. Hoplocr. dipentas, 1867, 

 Grevingk, Tiber, Hoplocr. dipentas and Baerocr. Ungerni, p. 10, figs. 1 a-f; 

 also Arch, fiir Naturk. Liv. Ehst. uuJ Kurlauds (Ser. i), Vol. iv, p. 110. 

 Hybocrinus dipentas, 1884, Schmidt, Memoires do I'Acad. Imp. des Sci. de 

 St. Petersb., Tome xxi, No. 11, p. 3, PI. i, figs. 4, 5, 6 ; also Carpenter, 1882, 

 Quart. Journ. Geol. Soc. London (August), pp. 298-312. Hoplocr. dipentas, 

 1883, W. and Sp., Amer. Journ. Sci., Vol. .\xvi (November), p. 365. 

 Vaginaten Kalk., Low. Silur. Pulkowa, Russia. 



HYBOCRINUS Billings. 



1857. E. Billings, Geol. Surv. Can. for 1853-56 (Rep. of Progr.), p. 275. 

 1859. E. Billings, Geol. Surv., Decade iv, p. 23. 

 1879. Zittel, Handb. d. Palieont., i, p. 350. 



1879. W. and Sp., Rev. of the Palaeocr., i, p. 74. 



1880. Wetherby, Journ. Cincin. Soc. Nat. Hist. (July). 



1882. Carpenter, Quart. Journ. Geol. Soc. London (Aug.), pp. 298-312. 



1883. W. and Sp., Amer. Journ. Sci., Vol. xxvi, p. 365. 



When we defined Hybocrinus., Rev., Pt. i, p. 74, we regarded it as 

 synonymous with Hoplocrinus and Baerocrinus, wliich, we have 

 since shown, are generically distinct. However, in our late 

 paper in the Amer. Journal we made some remarks upon the 



