328 Cincinnati Society of ISFatural History. 



Dr. Wachsmuth, the habit of the species, and indeed of the genus, 

 being such as to give the arms and like parts a comparative!}^ short 

 and strong character. 



The Column. — This is small, pentagonal, and composed of nearly 

 equal plates, which are alternately larger and smaller near the body, 

 2:iving the column a ringed appearance. 



As but an inch or two of the column has been observed, further 

 characters can not be given it. The proximal portion is invariably 

 bent to one side of the columnar cavity, and in contact with its 

 plates. 



Of this species I have found many specimens of various ages and 

 sizes, of which the essential characters are given above. Some of the 

 younger specimens have the spines very beautifully preserved, and it 

 seems that this character of ornamentation reached its maximum of 

 development in che curious crinoid above described. 



Hydreionocrixus armiger, Meek and Worthen (Wachsmuth non 



Wetherby). 



Under-basals — Five, small, outwardly entirely concealed b}^ the 

 base of the column, which almost completely fills the small excavation; 

 inwardly they have much the same construction as in the species 

 aboA'e described. 



Basals — Five, three pentagonal, the two on the azygons side hex- 

 agonal, being made so by the truncation of their upper extremit}'', 

 upon which the lower plates of the azygous scries rest. They are 

 nearly equal in size, and flexed in the middle so that one extremity 

 points upward into the columnar excavation, and the other upward 

 upon the outside of the body; this gives the central part of these plates 

 a convexitj^ which imparts to the base of this species one of its dis- 

 tinouishino- features. 



liadials — Five, pentagonal, wider than high, equal in size, and each 

 articulated across its entire upper face with the brachial of the same 

 ray, as niiiy be seen in plates 7 and 8. 



Brachials — Five, pentagonal, wider than high, and each bearing 

 upon the upper sloping sides the large plates of the arm series as in 

 the species above described. Each of these plates has its outer sur- 

 face, at the upper angle, prolonged, into a stout spine, as may be 

 seen from figure 7. The upper part of these plates, forming the base 

 of the spines, is much thickened, so that the bod}' of the crinoid grad- 

 ually widens upward to this point as shown by figures 7 and 8. 



Arms — Ten, resting upon the sloping upper surfaces of the 



