INVERTEBRATES. 185 



Genus ZEACRINUS, Troost. 



Synon. — Cupressocrinus (sp.), McCoy, 1849. Ann. Mag. Nat. Hist., 2d Ser., Vol. ii, p. 



244; (not Goldf., 1832.) 

 Poteriocrinus (sp.), deKoninck and Lehon, 1854. Recherch. Crinoides, p. 91 ; 



and of some others. 

 Hydreionocrinus (sp.), de Koninck, 1858. Bull. Acad. Royale Belgique, 2d Ser., 



t. iii, p. 19. 

 Zeacrinus (Troost), Hall, 1858. Iowa Report, Vol. i, part 2d, p. 541. 



Generic formula. — 



Basal pieces, 5, small, and often hidden by the column. 



Subradials, 5. 



Radials, 2+5, or often 3, 4 or more, in the anterior ray. 



Anal pieces, 4 to 6 or more, visible between the arms. 



Interradials, 0. 



Arms, 10 to 40. 



The species embraced in this group have the body rounded 

 below, with the five very small basal pieces sunken in a con- 

 cavity, and often nearly or quite hidden by the column. The 

 five* subradials are sometimes long, narrow, suboval or lanceo- 

 late, with a more or less pentagonal outline, excepting one on 

 the anal side, which is often hexagonal. The primary radial 

 series all alternate with the subradials, and are so wide as to 

 connect laterally, so as to leave no spaces for interradial pieces; 

 each consisting of two pieces, excepting in the anterior ray, 

 which has usually three or more. Anal pieces, from four to 

 six or more visible between the arms — two to three of them 

 forming a part of the wall of the cup below the arms, as in 

 Poteriocrinus. Summit unknown. 



The species composing this group, although differing in general appearance, 

 are closely related in structure to Poteriocrinus, but, as already stated in the 

 remarks upon that genus (page 181), they differ in having the body rounded 

 below, and the base very small and sunken; the arms are also usually less 

 elongated and broader, as well as always with only two primary radial pieces, 

 excepting in the anterior ray, which generally has more. Unfortunately we 

 know nothing of the structure of the vault in this group, though judging from 



* In one species (Z. elegans, Hall,) there is apparently an abnormal sixth subradial. 

 24 Ato. 31, 1866. 



