756 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



Dichocrinus polydactylus Casseday and Lyon. 

 Plate LXXVII. Figs, la, h. 



I860. Casseday and Lyon ; Proceed. Amer. Acad, of Arts aud Sci., Vol. V., p. 18. 

 1881. W. and Sp. ; Revision Pateocr., Part II., p. 84. 



Sjn. Dichocrinus expansus Meek and Wouthen (not De Koniuck and Le Hon 1853) ; Proceed; 

 Acad. Nat. Sci. Phila., p. 314 ; also Geol. Rep. Illinois, Vol. V., p. 500, Plate 14, Tig. 1. 



Of the type of D. lachrymosus. Calyx expanding rather rapidly along the 

 basals, thence more abruptly to the top of the radials, where its width is once 

 and a half its height. The calyx in a dorsal aspect is sharply hexagonal, 

 owing to the convexity of the radials and anal plate, especially in the upper 

 parts where the median portions are conspicuously gibbous, producing an 

 angular depression along the interradial sutures. The basi-radial and inter- 

 basal sutures are also slightly grooved, and the margins of the plates some- 

 what beveled. Surface of plates ornamented with scattered, irregular, 

 wart-like nodes, which show a tendency to form vertical rows. Similar 

 markings occur upon the radials, where they start from the projecting 

 upper rim and run to the lower end of the plates. 



Base large, its height almost one half that of the entire cup ; its lower 

 face surrounded by conspicuous nodes, which are sometimes confluent and 

 form a rim around the lower margin. Eadials nearly twice as wide at the 

 upper end as at the lower, the upper face almost equal to the length of the 

 plates ; the fiicet bounded by a heavy, thickened rim. Anal plate wider and 

 longer than the radials, sti'ongly convex in the middle, somewhat inflected 

 at the top. Costals two, twice as wide as long. Distichals three ; the first 

 and second, like the first and second costals generally united by syzygy, 

 their suture lines being less distinct than those between the other brachials ; 

 the third distichal largest and axillary ; it supports on its outer face a simple 

 arm, which slopes obliquely upward, and on the inner face two palmars 

 arranged almost in vertical line with the distichals, and resembling them in 

 form and size. The second palmar bifurcates again, giving off in the same 

 manner as the preceding axillary an arm from the outer side, and from the 

 inner two or three post-palmars, which support two simple arms, making 

 four arms from each main division, or eight from each ray. Arms biserial 

 from the fourth or fifth plate; they are long, rounded on the back, and 

 taper verj' slightly ; pinnules closely set and of moderate length. Ventral 

 disk higher than the dorsal cup, composed of comparatively large plates; 



