1886.] NATURAL SCIENCES OP PHILADELPHIA. It5 



and like them has large basals, comparatively small radials, and 

 an unusually large azygous plate, followed by the anal piece and 

 proximal plate of the ventral tube. It differs, however, from 

 both genera in the number of underbasals, and the peculiarities 

 in the radial regions which have been mentioned. 



Revised Generic Diagnosis. Dorsal cup globose ; composed of 

 heavy plates. Underbasals three, comparatively large ; two of 

 them larger than the other, but not of equal size ; the smaller 

 piece placed in a vertical line with the anterior radial (PI. 6, fig. 

 5). Basals five, extremely large, very irregular in form; the 

 posterior one heptagonal and larger than any of the rest ; that to 

 the left pentagonal ; the three others hexagonal. The upper side 

 in four of the plates is angular, in the other truncate, supporting 

 the right posterolateral radial. 



Radials five ; irregular in form and size, the postero-lateral one 

 considerably smaller than the others. The two posterior radials 

 as well as the anterior one pentangular, truncate above, and 

 they support a short subquadrangular brachial ; the two antero- 

 lateral ones hexagonal, angular above, supporting on each side an 

 arm. The line of articulation between the three former radials 

 and their respective brachials is widely gaping, and the mode of 

 articulation similar to that of all later Poteriocrinidse. The 

 brachials, although short, are twice as wide at their union with 

 the radials as along their upper ends, which are truncate, moder- 

 ately concave, each supporting a single arm. The two other 

 radials, which have angular upper faces, are slightly constricted 

 along their upper ends so as to indicate an anchylosis of 

 brachials and radials. 



Nothing is known of the ventral surface except imperfect 

 impressions of small pieces. The azygous plate is unusually 

 large, subquadrangular or trapezoidal ; placed obtusely between 

 the posterior basal and the right postero-lateral radial ; its upper 

 angle, which extends almost to the top of the radials, is slightly 

 truncated and supports the ventral tube, its left upper side abuts 

 against a large subquadrangular anal plate. Column apparently 

 small and circular. 



1847. Tribrachiocrinus Clarkei (Type of the g^nus) McCoy, Ann. and Mag. Nat. 



Hist., Vol. XX, p. 228, PI. 12, Figs. 2, a.b.c.-Pictet 1857, Traite de Paleont., 



Vol. IV, p. 321. Carboniferous. Australia. 

 1884. T. corrugatus Rs^tte, Proceed. Linnean Soc. of New South Wales, Vol. IX, Pt. 



4. Carboniferous. Australia. 



