ECHINODERMATA—CRINOIDEA. 493 



tegminal they are on the surface of the disk. The ambulacra 

 contain the food-grooves. In most Camerata the ventral disk is 

 pierced by a succession of small respiratory pores near the arm 

 bases. 



The plates of the crinoid are united by suture or by muscular 

 articulation; when anchylosed the sutures are close, with the 

 lines of union obliterated by subsequent lime deposit. 



The subdivisions into orders is based largely on the part that 

 the lower brachials take in the dorsal cup and their manner of 

 union with it. In the Camerata the lower brachials take part in 

 the dorsal cup and all plates of the calyx are united by close 

 suture. In the Flexibilia and Articulata, the lower brachials 

 are incorporated into the dorsal cup but all plates from the radials 

 up are movable and the mouth and ambulacra are tegminal. In 

 the two other orders the arms are free above the radials, the 

 FiSTULATA being distinguished by the presence of the ventral sac 

 and by tegminal ambulacra, and the Larviformia by the ventral 

 disk composed of orals only, with subtegminal ambulacra. 



Literature. 



1858. Hall, James. Geol. Surv. Iowa, i. 



1859. Hall, James. Pal. N. Y., 3 (Helderbergian). 



1859. Billings, E. Can. Org. Rem. (Ordovicic), Decade 4, Geol. 



Surv. Can. 

 1875. Meek and Worthen. Geol. Surv. 111., V. and VI. 

 1879-86. Wachsmuth, C, and Springer, F. Revision of the 



Paleo-Crinoidea, I.-III. (Proc. Acad. Nat. Sci. Phil.). 

 1897. Wachsmuth and Springer. The North American Crinoidea 



Camerata. Mem. Mus. Comp. Zool. (Describes and figures all 



known North American Camerata.) 

 1900. Weller, Stuart. Crinoidea of Chicago Area (Niagaran). Chic. 



Acad. Sci. Bull., 4. 

 1904. Schuchert, Charles. On Camarocrinus. Smith. Misc. 



Coll., 47, 253-272. 

 1904. Wood, Elvira. On New and Old Middle Devonic Crinoids. 



Smithsonian Miscellaneous Collections, pp. 56-84, pis. XV.-XVI. 

 1909. VJood, Elvira. A Critical Summary of Troost's Unpublished 



Manuscript on the Crinoids of Tennessee. United States National 



Museum, Bull. 64, pp. 1-150, pis. I. -XV. 



