352 PROCEEDINGS OP THE ACADEMY OP [1879. 



1859. Zeacr. ovalis Lyon and Casseday. Am. Jour. Sci. (n. 8.) vol. 29, p. 71. Ches- 



ter limest. Subcarb. Ky. 



1858. Zeacr. ramosus Hall. Geol. Rep. Iowa, vol. i, pt. ii. p. 548, pi. 9, fig. 3. 

 Upper Burl, limest. Subcarb. Burlington, Iowa. 



1869. Zeacr. scobina Meek and Worthen. Proc. Acad. Nat. Sci. Phil., p. 149; 

 Geol. Rep. 111., vol. v. p. 426, pi. 1, fig. 2. Upper Burlington limest. Sub- 

 carb. Burlington, Iowa. 



1869. Zeacr. serratus Meek and Worthen. Proc. Acad. Nat. Sci. Phil., p. 151 ; 

 Geol. Rep. 111., vol. v. p. 428, pi. 1, fig. 6. Upper Burlington limest. Sub- 

 carb. Burlington, Iowa. 



1860. (Sept.) Zeacr. Troostanus Meek and Worthen. Proc. Acad. Nat. Sci. Phil., 



p. 390; Geol. Rep. 111., vol. ii. p. 186, pi. 16, fig. 2. Upper and Lower 



Burlington limest. Subcarb. Burlington, Iowa. 

 (Sy>i.) Zeacr. scoparius Hall (Feb. 1861). Descr. New. Pal. Crin., p. 8; 



Bost. Jour. Nat. Hist., p. 305. 

 (Syn.) Zeacr. sacculus White (1862). Proc. Bost. Soc. Nat. Hist., p. 12. 

 1858. Zeacr. wortheni Hall. Geol. Rep. Iowa, vol. i. pt. ii. p. 683. Chester limest. 



Subcarb. Chester, 111. 



(Compare with Z. magnolieeformis.) 



18. HYDREIONOCRINUS De Koninck. 

 1858. Bull. Acad. Royale Belgique, vol. viii. pt. ii. p. 13. 



A. Typical form. 



General form subcylindrical, short, slightly spreading toward 

 the tips of the arras ; with an enormous ventral sac extending be- 

 yond the limits of the arms, and covering them like a roof. 

 Calyx short, rounded below, basal portion sometimes deeply 

 concave. 



Underbasals small, and, according to De Koninck, forming a 

 five-rayed star or shallow cup. In all known American species 

 the underbasals rest within a deep concavit} r , and are scarcely 

 visible beyond the column; but they appear to be considerably 

 larger on the interior of the calyx, sometimes almost exceeding 

 the basals in size. Basals five, three of them of equal size, and 

 hexagonal ; the two in contact witli the anal plates frequently 

 larger. Radials five, large, much wider than high, four of them 

 pentangular, that on the left posterior side quadrangular; the 

 former resting each between two adjacent basals, and the latter 

 abutting upon 011I3' one. Brachials one to the ray, or two in the 

 anterior ray, pentangular, as large or larger than the radials, often 

 produced into long spines ; in species where the anterior ray has 

 an additional brachial, the first is quadrangular, the second is 

 pentangular and bears the spine. The brachials meet laterall}', and 



