INVERTEBRATES. 179 



The very prominent central portions of the subradial pieces are truncated 

 below on a plane with the base, and project out horizontally from it in such a 

 manner as to form a distinct five-rayed star, as seen from below. From near 

 the middle of each subradial there is a rather obscure angular ridge, extending 

 along each side of its prominent central portion to the base, and others con- 

 necting with similar ridges on the first radials and anal piece above. The very 

 profound excavations between the prominent central portion of the subradials 

 extend in so as to produce a slight emargination in the outer extremity of each 

 basal piece, while the depressions between the first radials produce a similar 

 indentation in the extremity of each subradial. Judging from the obliqueness 

 of the superior truncated side of the first radial plates, it is manifest that the 

 succeeding radials must have extended very obliquely outwards and upwards. 



Prof. Hall's Supplement to the Iowa Report did not reach us until our 

 description of this species, published in the Proceedings of the Academy of 

 Sciences, was in type ; and from the necessarily hurried manner in which we 

 were then compelled to make comparisons, we overlooked the identity of the 

 form under consideration with his Cyathocrinus sculpiilis. The fact that he 

 had described the first anal plate as being "heptagonal," and the second "quad- 

 rangular," with its" "upper margin on a line with the summits of the adjacent 

 radials," led us to think our specimen clearly distinct. A subsequent more 

 careful comparison, however, with his diagram (page 60, Supplement to Iowa 

 Report), has satisfied us that he had inadvertently described one of the subra- 

 dial pieces as the first anal plate, and the first anal piece as the second. When 

 these corrections are made in his description, it agrees so very nearly with our 

 crinoid that we can scarcely entertain a doubt of their identity. 



Locality and position: Burlington limestone, Burlington, Iowa. 



Genus POTERIOCRINUS, Miller. 



Synon. — Encrinus and Astropodia (sp.), Uee, 1793, Hist. Rutherglen. 



Poteriocrinites, Miller, 1821, Nat. Hist. Crinoidea, p. 68; Schlot., 1823, Naturg. 

 Z. Petref. Th. 1, p. 82; Blainv., 1834, Man. Act., p. 260, and various others. 



Poteriocrinus, Agassiz, 1834. Mem. Soc. Sci., Neuch., p. 197, and most sub- 

 sequent authors. 



? Scaphiocrinus, Hall, 1858. Iowa Report, vol. i, part ii, p. 550. 



? Coeliocrinus, White, 1863. Boston Jour. Nat. Hist., vol. vii, p. 499. 

 Generic formula. — 



Basal pieces, 5. 



Subradials, 5. 



Radials, 1 (large) -4- 5, and a variable number of smaller ones. 



Anals, 4 to 6. 



Arms variously divided, according to the species. 



Vault, greatly produced in the form of a large proboscis. 



