TROOST 's CRINOIDS OF TENNESSEE E. WOOD. 



33 



the posterior ambulacra and inter ambulacrum. The interambula- 

 crals are the largest plates of the tegmen. There are four or five of the 

 large plates, ornamented by tubercles, and several smaller accessory 

 pieces. Troost's description applies to the right antero and postero- 

 lateral interambulacral areas, but the others are less regular. The 

 ambulacral areas are covered by two rows of small convex plates. 

 About halfway from the center to the margin each area divides, 

 giving rise to two branches with a double series of minute covering 

 pieces. Each of these again divides, its inner branch going to an 

 arm base and the outer terminating on the upper surface of a small 

 second interbrachial. Near the margin still another branch passes to 

 the upper surface of the second secundibrach. 



This species is distinguished from Marsipocrinus tennesseensis by 

 its small size, the character of the tegmen plates, and the surface 

 ornament. 



Formation and locality. — Brownsport limestone. Decatur County, 

 Tennessee. 



Cat. No. 39924, U.S.N.M. 



MARSIPOCRINUS STRIATUS (Wachsmuth and Springer). 



Plate 9, figs. 13, 14. 



Cupellsecrinites striatus Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 1850, 



p. 61 (nomen nudum); MSS., 1850. 

 Cupellsecrinites infiatus Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 1850, 



p. 61; MSS., 1850. 



Cupellaecrinus striatus Shumard, Trans. Acad. Sci. St. Louis, II, No. 2, 1866, 



p. 362 (catalogue name). — Wachsmuth and Springer, Rev. Palseocrinoidea, 



II, 1881, p. 230 (catalogue name). 

 Cupellxcrinus infiatus Wachsmuth and Springer, Rev. Palseocrinoidea, II, 1881, 



p. 230 (catalogue name). 

 Marsupiocrinus striatus Wachsmuth and Springer, North Amer. Crinoidea 



Camerata, 1897, p. 732, pi. lxxv, figs. 17, 18. 



The name striatus was first proposed by Troost for a species of 

 Marsipocrinus in 1850. 

 His description is as follows: 



I found only one partly complete specimen of this species. Detached pelvic [basal] 

 plates are rather abundant, they are generally large, some as much as 30 mill. m. in 

 diameter, divisible into three parts, not depressed towards the centre as in the C. Isevis 

 [Marsipocrinus tennessensis] but rather convex. The alimentary aperture [lumen] is 

 pentalobed and is surrounded with an elevated circular border. They are striated, — 

 the stria running at right angles from the margin of the plate. 



- Some, perhaps the same species, have five rays running from the centre towards the 

 circumference. 



Observations. — The basal plates here described differ from those of 

 Marsipocrinus striatus Wachsmuth and Springer in being convex 

 instead of concave, and they may belong to a different species, but in 

 the absence of the specimens it is impossible to determine this with 

 63330—09 3 



