ACTINOCRINID^. 561 



Actinocrinus pernodosus Hall. 

 Plate, LY. Fkjs. 2a,l. 



1858. Hall; Geol. Rep. Iowa, Vol, I., P:iit II., p. 60S, Plate 15, Figs. 3*, b, andPIalc 16, Pig. 7. 

 18S1. W. aud Sp. ; Revision Palajocr., Part II., p. 145. 



Nearest to A. verrucosus, but of larger size, the plates heavier and de- 

 cidedly more nodose. Calyx a little higher than wide, uniformly spreading 

 from the broadly truncated base to the top of the second costals, whence the 

 rays spread obliquely outward. The iuterbrachial spaces curve slightly 

 inward, and form deeply depressed areas, which give to the calyx from a 

 ventral aspect a strongly pentalobate outline. Tegmen short, depressed 

 convex. Plates of the dorsal cup massive and highly elevated, the surfaces 

 rising obliquely from the suture lines to near the centre of the plates, and 

 thence abruptly to their summits, there forming conspicuous nodes, which 

 upon the radials and brachials are transversely arranged. From these 

 nodes, broad ridges proceed to adjoining plates, two — exceptionally three — 

 from the radials to the basals, while there is but one between the other 

 plates. These ridges and nodes give to the surface a rugose and rough 

 appearance. 



Basals large, projecting outward, and forming with their lower margins a 

 strong rim around the top of the column, which is deeply notched between 

 the jjlates. Eadials as long as wide, or longer ; their sloping u^jper faces 

 much shorter than the lateral ones. First costals less than half the size of 

 the radials, nearly as long as wide ; the second as wide as the first, but only 

 half as long. Distichals small, giving off an arm to one side, and two pal- 

 mars to the other ; the latter supporting on their axillary two arms, which 

 are free from the second plate. Distichals and palmars quite short, angular 

 on the back, and separated from adjoining brachials of the same ray by deep 

 grooves, formed by the incurving sides of the plates. Arms six to the ray, 

 stout, long, and apparently simple throughout. Regular interbrachials : 1, 

 2, 3, followed by a number of smaller plates, which gradually pass into 

 interambulacrals, and decrease in size upwards. The anal plate, which is 

 smaller than the radials, is followed by 2, 3, and 5 pieces. There are no 

 interdistichals between the main divisions of the rays. Orals and all ambu- 



71 



