382 PROCEEDINGS OF THE ACADEMY OF [1888. 



a considerable departure from the typical form of the genus. It is 

 inconsistent with the generic definition of Angelin, who described it 

 as having 'Hnterracllalla nulla." It is a variation in the direction 

 of the English form of Marsxipiocrinus — M. coelatus — (PL XX, fig. 

 7), which differs in its dorsal interradials from M. tennesseensis in al- 

 most the same way. 



Crotaloerlnus and Enallocrmus form a good family, which is con- 

 nected through Marsupiocrinus ^ with the other Camarata. 



Suborder CAMARATA. 



Family CROTALOCRINIDAE. 



Base dicyclic, symmetry bilateral. Calyx throughout composed 

 of rigid plates. Dorsal cup constructed almost exclusively of under- 

 basals, basals, the first radials, and a small anal j^late. Higher 

 radials uj) to the third or fourth order irregularly Avedge-shaped, 

 their sharp ends directed outwards or sometimes hidden from view, 

 their larger ends, wdiich curve upwards, grooved for the ambulacra. 

 The plates rest partly upon the first radials, partly against the radials 

 of the preceding ()rder, being with the former, and with one another, 

 and laterally with those of adjoining rays, firmly united by suture. 

 Arms capable of great mobility ; uniserial ; long ; dividing into very 

 numerous branches, wdiich are free, or connected laterally by tis- 

 sues so as to form a net-work around the calyx, either continuous, or 

 limited to the rays and forming five reticulate leaf-like arms. The 

 arm branches are perforated by large axial canals, which penetrate 

 also the higher radials. 



Ventral surface of calyx flat, composed of five unequal orals — the 

 posterior one the larger — five radial dome plates, one or more inter- 

 radials, and several series of covering pieces which take the rigid 

 form of vault plates. 



Column large, round ; central cavity extremely large. 



CROTALOCRINUS Austin. 



1842. Austin, Ann. and Mag. Nat. Hist., Ser. 1, Vol. X, p. 109. 



1843. Austin, ibid., Ser. 1, Vol. XI, p. 198. 



1848. Morris, Cat. Brit. Fos. (Ed. 1), p. 50 ; (Ed. 2), p. 75. 



1 It is an interesting fact as showing the keen perception of that veteran 

 English naturalist, that Th. Austin in 1843 (Ann. and Mag. Nat. Hist. Sen, II, Vol. 

 XI, p. 198) referred C. rtcgosiis to the Marsupiocrinidae, a family named, but not 

 defined by him. 



