PLATYCEINID^. - 731 



C. inflatiis, C. Icevis, C. magnificus, C. pentagonalis, C. rosceformis, C. stellatus, 

 and C. striatus, — all from Decatur Co., Western Tennessee — which in all 

 probability are mere varieties of ^larsiqnocrinus tennesseensis (Roemer). A 

 figure of the ventral side of 31. depressus Ang., from the Upper Silurian of 

 Gotland, Sweden, is given on Plate III., Fig. 23. 



Marsupiocrinus tennesseensis (Eoembe). 

 Plate LXXV. Figs. 16a, h. 



1860. Platvcrinm tennesseensis — Roemek; Silur. Fauna West. Teuu., p. 35, Plate 3, Figs, ia h, c 



'd.e,/. 

 18S1. Marsupiocrinus tennesseensis — W. and Sr. ; Revision., Part II., p. 65 (Proceed. Acad. Nat. Sei. 



PhUa., p. 239). 



A rather large species. Calyx greatly depressed, its width about twice 

 its height, the latter equally divided between cup and tegmen. Dorsal cup 

 sancer-shaped, the base flat, the sides slightly convex, rapidly spreadino-. 

 Plates moderately thin and flat, the ornamentation somewhat variable. In 

 the majority of specimens the surface of the plates densely covered with 

 somewhat irregular, very fine, closely arranged, longitudinal and transverse 

 striss ; the longitudinal ones running in almost parallel lines from the upper 

 edges of the radials to the foot of the basals ; the transverse ones, which are 

 restricted to the lateral margins of the radials, traverse the sutures, and meet 

 the longitudinal ones at an angle ; the successive angles, as they follow the 

 plates, forming an oblique line from the top of the radials to their lower 

 angles. In other specimens the strise are broken up into rows of small 

 nodes, some of which are round, but most of them elongate, giving to the 

 surface a peculiar rugose appearance. Sutures not grooved, and often 

 difficult to see. 



Basals spreading horizontally, forming a flat, sharply pentangular disk; 

 the column facet surrounded by a small, circular ridge, and the space within 

 slightly excavated; the axial canal rather large and pentagonal. Radials 

 hexagonal ; greatest width to length as seven to four, rapidly spreading to 

 two thirds their height, the upper faces almost straight, being but very 

 slightly indented for the reception of the costals ; the sloping upper faces 

 forming a deep notch with corresponding faces of adjoining plates. Costals 

 extremely small even for the genus, trigonal, a little wider than long. 

 Distichals two, quite unlike in form and size ; the first rather large and sub- 

 lunate, one of its sides abutting against the costals and meetinsr above with 



