﻿2l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vol. 47 



Column unknown. 



Genotype, T. chrysalis n. sp. The only other species is T. fenes- 

 trates (Troost). 



As in Staurocystis, Tetracystis has the same arrangement of the 

 thecal plates and of those in the anal area, but differs widely in the 

 construction of the ambulacra. In the latter they are slender, incon- 

 spicuous, each with about 20 brachiole sockets, while in the former 

 the ambulacra are wide, very conspicuous, heaped medially, and each 

 bears about 40 brachioles. Moreover, deltoid 23 is a prominent plate 

 in Tetracystis, while in Staurocystis it is probably very small, the 

 relation of this genus being with Pseudocrinitcs. Apiocystitcs is also 

 closely related to Tetracystis, but differs in having the 2 parts of 

 each pectinirhomb discrete and the anal plates surrounded by thecal 

 plates 7, 8, and 13; while in Tetracystis there is an additional plate, 

 or 7, 8, 13, and 14. Lepocrinites differs in having but 3 thecal plates 

 bounding the anal area instead of 4 as in the new genus. In Jackcl- 

 ocystis plate 19 is lacking, the rhombs are quite different, and the 

 anal area has not a second circle of small pieces as in Tetracystis. 



TETRACYSTIS CHRYSALIS n. sp. 

 (Plate XXXIV, figures 9, 10; Plate XL, figures 1-3) 

 Length of theca of holotype 23 mm. ; width 17 mm. ; depth 13 mm. 

 A single paratype has a length of 24 mm.; breadth 15 mm.; depth 



Fig. 25. — Analysis of Tetracystis chrysalis n. sp. 



13 mm. For general form, shape of individual plates and their 

 ornamentation, see the figures and diagram, figure 25. 



Ambulacra narrow, depressed, not excavated into the thecal plates, 

 and extending to the column. Ambulacrals very long and nar- 

 row, about 20 in a column. Ambulacralia extremely small, about 12 

 to 14 to each ambulacral. Brachioles very slender, about 11 on 

 each side of an ambulacrum or about 88 to each theca ; length un- 

 known. 



