ACTINOCRINID^. 571 



Actinoerinus tenuiseulptus MoChesnet. 

 Plate LV., Figs, j^, b. 



1859. McChesnet; Descr. New Spec. Palseoz. Foss., p. 15. 



1867. McChesnet; Trans. Cliic. Acad. Sci., Vol. I., p. 11, Plate 5, Fig. 1. 



1881. W. and Sp. ; ReTision PaliBocr., Part XL, p. 146. 



Sju. Aetinocrimis chloris Hall — 1861; Boston Journ. Nat. Hist., Vol. VII., p. 275. 



A moderately small species, which, in the delicacy of the plates of the 

 calyx, the beauty of their ornamentation, the spiniferous character of the 

 plates in the tegmen, and the long hooks upon the pinnule joints, reminds 

 us of certain forms for which we have proposed the genus Cactocrinus. The 

 calyx, however, is distinctly lobed, and the arms are arranged in clusters, 

 which are separated by wide and deep depressions or grooves extending far 

 up into the ventral disk, and the upper bifurcations of the ray take place 

 from two successive palmars. Dorsal cup semiglobose, truncate at the base, 

 with a small rim around the lower margin, the sides convex to the top of 

 the distichals, thence slightly more spreading to the arm bases. Tegmen 

 almost as high as the dorsal cup, subpyramidal ; cross-section at the arm bases 

 broadly quinquelobate. Plates of the dorsal cup slightly tumid, covered 

 by radiating ridges with undulated edges, wider at the middle of the plates 

 than at their margins. The ridges passing up and down the radials and 

 brachials considerably the strongest, dividing the surface of the calyx into 

 five well defined fields, which extend from the basal ring to the bases of the 

 free arms, and enclose a well marked star at the four regular sides, while the 

 anal side contains two somewhat smaller stars with seven rays. 



Basals short, the projecting rim subcircular or obscurely trilobate, accord- 

 ing to the greater or less depth of the sutural depression. Eadials from 

 one fifth to one third wider than long. First costals half the size of the 

 radials, quadrangular, and nearly twice as wide as long ; the second hep- 

 tangular, wider and longer in proportion, obtusely angular above. Distichals 

 rather small, all axillarj', giving ofif an arm to the outer side, and two small 

 palmars which support two arms to the other. Arm facets small, but the 

 ambulacral openings comparatively large. Arms six to the ray, slightly 

 angular below, gradually flattening above; the tips incurving. The four 

 proximal arm joints are in single series, as long as wide, and even longer; 

 they are cuneate, and each one has at its upper end from its longer side 



