678 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



torted, much smaller specimen, with smooth plates. In the type of P. p-at- 

 tenanus, which preserved its natural form, the rim around the base projects 

 more than in the type of P. Sara as figured by Hall, but the base is not 

 correctly represented in that figure. P. monroensis is a very young speci- 

 men in which the arms are as yet uniserial, zigzag, and the plates -wedge- 

 form, with nothing to indicate that it differed from the jjreceding forms. 



Platycrinus Huntsvillse Troost MS. 

 Plate LXXIII. Figs. 6, 7a, h, 8, 9, 10, 11, 12. 



1819. Troost; Proceed. Amer. Ass, Adv. Sci. of 1849, p. 61 (without descriptiou). 



Sjii. Plati/crimis penicillus M. and W., ISCO ; Proceed. Acad. Nat. Sci. Phila., p. 380 ; also Geol. 



Rep. Illinois, Vol. II., p. 266, Plate 19, Tigs. 6«, b, c. 

 Syn. Flat^crimis pleirus M. and W., 1860 ; Proceed. Acad. Nat. Sci. Phda., p. 380 ; also Geol. Rep. 



Illinois, Vol. II., p. 267, Plate 20, Fig. 3. 

 Syn. Platycrinus alabameiisis S. A. MiLLEE, 1891 ; Adv. Slieets 17tli Rep. Geol. Surv. Indiana, p. 50, 



Plate 9, Pig. 5. 



An extremely variable species of the type of P. Saras, varying consid- 

 erably in the form and ornamentation of the calyx plates and in the number 

 of arms ; but readily recognized by the peculiar and unique form of the 

 brachials, and the presence of a large pinnule upon the first distichals and 

 first palmars. Dorsal cujd generally a little wider than high, cup or bowl- 

 shaped ; the sides in most of the specimens nearly straight, curved longi- 

 tudinally, but sometimes distinctly convex and constricted at the arm 

 regions ; base of the ctip rather broadly truncated. 



Basals forming a short saucer-shaped cup with a flattened or slightly 

 concave lower face, which exceeds the width of the stem at the upjjer end ; 

 the interbasal sutures visible by moistening the specimens, theu* lines highly 

 elevated above the surface, and formed into ridges which at the lower edges 

 of the cup terminate in small tubercles. Eadials subquadrangular, about as 

 wide as long in mature specimens, proportionally a little .shorter in the 

 younger ones; the sides very slightly expanding; the superior lateral angles 

 distinctly truncated. Facets directed upward; small, occupying onl}' one third 

 the width of the plates, and extending but a short distance downwai-d. Cos- 

 tals trigonal, much wider than long, occupying the full width of the facets ; 

 the superior faces concave, and indented at the median portions for the 

 reception of small processes passing out from the lower edges of the dis- 

 tichals, and forming waving sutures, which resemble those of the Ichthj'o- 

 crinidse. Similar suture lines occur between the distichals, palmars, and 



