SAGENOCRINIDAE 253 



Forbesiocrinus burlingtonensis n. sp. 



Plate XXVI, figs. 3-5 



I have separated under this name those specimens occurring in the Bur- 

 lington rocks which have three primibrachs. The description of F. agassizi 

 will apply to them in other respects save two ; ( 1 ) the extreme sinuosity of the 

 brachial sutures which exists in all well-marked specimens; and (2) the size of 

 the specimens. The largest of the present form' is smaller than the smallest of 

 the other. Five representative specimens of F. agassizi, including the largest 

 and the smallest, compared with five similar specimens of the present species, 

 give the following average dimensions : 



F. agassizi: Height of crown, 96 mm. ; of calyx, 57; width, 65 ; base, 13. 



F. burlingtonensis: Height of crown, 59 mm.; of calyx, 29; width, 33; 

 base, 9. 



I have eight specimens of this species, in the largest of which the crown is 65 mm. 

 high ; calyx, 30 ; width, 43 ; base, 1 1 ; column at 20 mm. below, 8. In these eight specimens 

 26 rays are visible, and every one of them has three primibrachs. A single small specimen 

 not included in the above averages, only 27 mm. high, has in four visible rays 3 with 2 IBr, 

 and 1 with 3. This is the only case of individual irregularity I have found in either form. 

 Size alone, among specimens of the same locality, is ordinarily no criterion of a species ; but 

 in this case its correlation to such a degree of constancy with the number of primibrachs and 

 another character must be of more than ordinary significance. For these reasons I feel 

 warranted in separating these two forms, which are in fact far more easy to distinguish 

 than some of the Keokuk species heretofore described by others. There may be noted in 

 addition the tendency in this species to form a vertical row of anal plates, as shown on 

 Plate XXVI, figure 5 (the appearance of bifurcation on two plates in this figure is errone- 

 ous), which occurs not unfrequently in some of the Keokuk species, but which I have not 

 observed in F. agassizi. 



Types. Author's collection, except figure 4 which is in the Museum of Comparative 

 Zoology at Harvard College. 



Horizon and locality. Upper Burlington limestone ; Burlington, Iowa. 



Forbesiocrinus wortheni Hall 

 Plate XXVII, figs. 1-8 



Forbesiocrinus wortheni Hall, Geology Iowa, I, pt. 2, 1858, p. 632, pi. 17, fig. 5; Supplement Geology Iowa, 

 1859 (i860), pi. 3, fig. 7. — Meek and Worthen, Proc. Acad. Nat. Sci. Philadelphia, 1865, p. 140. — 

 Meek, Amer. Jour. Sci., ser. 3, VII, 1874, p. 191. — Wachsmuth and Springer, Revision Palaeoc- 

 rinoidea, pt. 1, 1879, p. 52. — Whitfield, Bull. Amer. Mus. Nat. Hist., 1882, p. 96. — Keyes, Geol. Surv. 

 Missouri, 1894, p. 224. 



Forbesiocrinus jerseyensis Miller and Gurley, Bull. 8, Illinois St. Mus. Nat. Hist., 1896, p. 58, pi. 4, 

 figs. 2, 3. 



Forbesiocrinus macadamsi Miller and Gurley, Bull. 9, Illinois St. Mus. Nat. Hist., 1896, pi. 5, figs. I, 2. 



Not Forbesiocrinus wortheni, Meek and Worthen, Geol. Surv. Illinois, V, 1873, p. 496, pi. 14, fig. 2, pi. 15, 

 fig. 7- 



A large species. Crown elongate with long arms. Rays moderately 

 rounded, in rather close contact above iBr; iBr areas slightly depressed. Calyx 

 moderately spreading to about IIBr 3 , where average height to width is i to 2 ; 



