I'lO PALJJONTOLOGY OF NEW-YORK. 



theless simple arms, or arms of a double series of plates, without armlets ; 

 while in the following species a further modification takes place, affecting 

 the structure of the bases of the arms, these appendages themselves 

 preserving the structure of those in M. plumosus. Further discoveries may 

 show some intermediate forms, by which these two extremes of develop- 

 ment may be united. 



The differences here indicated are not dissimilar in value to those on 

 which it is proposed to separate Ctenocrinus from Actinocrinus. The great 

 number of species under the latter genus renders such differences of more 

 interest than in a genus composed of few species, like the Mariacrinus. 



Mariacrinus (Subgenus) Teclinocriiius spinulosus ( n. s.). 



Plate LXXXV. Fio. 1 - 18. 



Body somewhat spheroidal, slightly contracted at the junction of the arms. 

 Basal plates four, small, wider than long; three pentagonal and one 

 hexagonal, marked by strong radiating ridges. First radial plates about 

 as long as wide ; three heptagonal, the others unknown. Second radial 

 plates hexagonal. Third radial plates pentagonal. Interradial plates (on 

 the side fully seen) four ; lower one regularly hexagonal. Brachial plates 

 double ; one resting on each sloping side of the third radial, and giving 

 origin to a pair of arms. Surface of plates ornamented by ridges and 

 nodes, or short spines. 



Akms composed at base of a single series of joints, becoming double above? 

 Tentacula unknown. 



Column somewhat pentagonal, consisting of joints which are deeply striate 

 on their articulating surfaces ; each alternate joint furnished with nodes 

 or short spines from the angles. 



This beautiful species is readily recognized from its general structiu-e, and from 

 its strongly ornamented surface. The column is obtusely five-angled; and from the 

 deeply striate articulating surfaces, and nodose or spiniferous angles, may be re- 

 cognized even in small fragments. The alternating joints are without nodes. 



The plates of the body, for three or more series above the base, are marked by a 

 central spine or node, which is surrounded by a series of smaller nodes, often, or 



