280 THE CEINOIDEA CAMEEATA OF NOETH AMEEICA. 



Basals five, forming an acute-angled pentagon. Radials large, wider 

 than long; lunate. Costals two; the first quadrangular; the second much 

 larger, almost as large as the radials. Distichals 2 X 10 in the calyx, the 

 others free arm plates. Arms ten, simple, uniserial, rather stout; pinnules 

 strong. Interbrachials : 1, 2, 1 ; the first very large, rising to the top of the 

 first costals. Anal area wider, containing three plates in the second and 

 third rows, and smaller ones above. Anus excentric, represented by a simple 

 opening, which faces laterally. Yentral disk low, the orals very large, occu- 

 pying in jS. captulum fully three fourths of the whole surface. Column 

 round. 



Distribution. — lIitheTto found only in the Upper Silurian of Gotland, 

 Sweden, but we now refer to this genus Walcott's Glyptocrinus argutus from 

 the Trenton limestone of New York, with some doubt. 



Remarks, — Angelin's descriptions and figures are so confusing that no 

 uniform generic characters can be deduced therefrom, unless some are elimi- 

 nated. Taking the first species S. capitiilum, Iconogr. Plate XVII., Figs. 

 5-5^, and the first figures of his second species 8. laevis, ibid., Plate XY., 

 Fig. 20, we have the type indicated by the above descriptions ; but Plate 

 XXYIIL, Figs, la, &, figured also as S. laevis, is clearly a Besmidocrinus, and 

 the specimen represented on Plate XXXIL, Figs. 3 and oa, is probably incor- 

 rectly figured, either as to the anal side or the arms. Plate XIX., Fig. 6, 

 figured as S. ovalis, is a totally different thing, and probably belongs to the 

 RhodocrinidoB. Plate XXL, Figs. 6, 7, described by Angelin as Harmocrinus, 

 and considered by us (Revision, II., p. 99) as belonging to Stelidiocrinus, has 

 very possibly a dicyclic base, and strongly resembles Tliysanocrinus. We have 

 not the material to settle these questions, but by restricting the genus to the 

 above mentioned forms, we have something tangible. The genus, as thus 

 defined, differs widely from any other of this group, especially in the struc- 

 ture of the disk, which is quite remarkable. The quadrangular first costal 

 distinguishes it from the associated genera with five basals. 



(?) Stelidiocrinus argutus (Walcott). 

 Plate XXIV. Fig. 6. 



1883. Gli/pfocrinus argutus — Walcott; 35tli Eep. N. Y. State Mus. Nat. Hist., Plate 17, Fig. 9. 

 1885. (?) Stelidiocrinus argutus — V\^. and Sp. ; Revision Palseocr., Part II., p. 103. 



Calyx small, somewhat pentangular; the interradial spaces depressed. 

 Basals five, rather large. Eadials subquadrangular, the upper faces moder- 



