250 



S M 1 T 1-1 SO N 1 A N I N ST I T U T 1 N 



Forbesiocrinus agassizi Hall 

 Plates XXI, fig. 2; XXV, figs. 1-6; XXVI, figs. 1-2 



Forbesiocrinus agassizi Hall, Geol. Surv. Iowa, I, pt. 2, 1858, p. 631, text-fig. 103 ; Supp. Geol. Iowa, i860, 

 p. 65 ; Bull. I, N. Y. St. Mus. Nat. Hist., Photo. Plates, 1872, pi. 7, figs. 1, 2.— Meek and Worthen, 

 Proc. Acad. Nat. Sci. Philadelphia, 1865, p. 140. — Wachsmuth and Springer, Revision Palaeocrinoidea, 

 pt. 1, 1879, pp. 45, 52; N. A. Crinoidea Camerata, 1897, p. 77. — Keyes, Geol. Surv. Missouri, IV, 

 1894, P- 22 4i pl- 3°i n g- 3- — Bather, Rep. British Assoc, for 1898 [1899], p. 923; Treatise on Zoology 

 (Lankester), pt. 3, 1900, p. 190.— Springer, Amer. Geologist, XXX, 1902, p. 89; Jour. Geology, XIV, 

 1906, p. 489. 



Forbesiocrinus Agassizi var. giganieus Meek and Worthen, Proc. Acad. Nat. Sci. Philadelphia, 1861 

 (1862), p. 131 ; Geol. Surv. Illinois, III, 1868, p. 495, pi. 18, fig. 3- 



A very large species. Crown elongate, 

 with long arms. Ravs stronglv convex and 

 prominent; iBr areas depressed. Calyx mod- 

 erately spreading from the column to greatest 

 width at about IIBr 3 , where average height to 

 width is about I to 1.6; height to width of calyx 

 at upper limit of iBr, 1 to 1 ; height to width of 

 crown, 1 to 0.67; height of calyx to crown, 1 to 

 1.6; spread of calyx from column facet, 1 to 5. 

 Cross-section at IIBr 3 obtusely pentagonal; 

 side outline curved. Surface smooth or finely 

 granulose. All calyx plates nodose or abruptly 

 elevated in the middle, while flat toward the 

 margin; those of iBr round, and of Br trans- 

 versely elongate. Brachial sutures deeply 

 sinuous, with patelloid processes large. Base 

 flush with column facet. Dimensions in milli- 

 meters of a very mature specimen with arms 

 folded at about the fourth bifurcation, and of 

 the smallest of fourteen specimens, similarly 

 folded, are as follows: Large specimen; height 

 of crown, 10 mm. ; of calyx to top of illBr, 65 ; 

 width of calyx, 62; of base, 18; column below 

 taper, 12. Small specimen; height of crown, 

 65 ; of calyx, 50; width of calyx, 50; of base, 12; column below taper, 8. Arms 

 of a large specimen outstretched to near the end, 85 mm. 



IBB flat like a columnal, without visible angles and scarcely distinguish- 

 able. Regular BB small, appearing as low pentagons, or as triangles; post. B 

 about as high as RR, angular above, with right shoulder the longest; it is fol- 

 lowed by two large anal plates, and these by others in ranges of 3, 4 and 5 

 abreast, gradually diminishing and passing into the tegmen at about the upper 

 IIIBr. First iBr about the size of first anals, followed by similar plates to the 



Fig. 35 

 Forbesiocrinus ogassiz 



