1881.] NATURAL SCIENCES OF PHILADELPHIA. 271 



more like that of Stelhliocrinus, which is composed of but few 

 and large plates. 



Zittel places Ilacrostijlocrinus with Dimerocrinus, Dolatocrinas 

 and Cijtocrinus under the Dimerocrinidfe. 



Generic Diagnosis. — Cal_yx subglobose to urn-shaped, as high or 

 liigher than wide ; surface granulose-striate, or only granulose ; 

 the five sides almost perfectl}^ equilateral. 



Basals three, comparatively lai'ge, forming a more or less shallow 

 cup, two of them equal and pentagonal, the third smaller by half 

 and quadrangular. Primary radials 3X5; the first series large ; 

 the second hexagonal, less than half, sometimes scarcel}^ one-third 

 the size of the first, wider than high ; the thii'd pentagonal, smaller 

 than the second, supporting one or more secondary- radials in a 

 direct line, which support the arms. Arms only known in M. 

 ornatus, where thej^ are long, simple, composed at the base of a 

 single row of alternately arranged wedge-form pieces, which, from 

 the sixtli or seventh plate up, interlock with each other, and gradu- 

 all}' pass into a double series. 



Interradial area more or less depressed, deeper between the 

 arm-bases, in consequence of which the radial portions of the calyx, 

 and especiallj^ the secondary radials, are somewhat lobed, which 

 is characteristic of this genus, and which distinguishes it readily 

 from the related form PateUiocrinus. First interradial large, 

 hexagonal, supporting two small plates in thft second series. 

 Anal area slightly wider, and with three plates in place of two in 

 the second range. 



Geological Position, etc. — 3Iacrostylocrinus is confined to the 

 Niagara group of America. 



The following species are known : 



*IS64. Macrostylocrinus Meeki Lyon. (Actinocr. Meeki). Proc. Acad, Nat. Sci. 



Phila., p. 411, PI. 4, figs. 4 a b. Niagara gr. Jefferson Co., Ky. 

 Syn. Cyathocr. fasciatus Hall. 28th Rep. New York St. Cab. Nat. Hist. (1st 



ed.), PI. 13, figs. 5 and 6 ; Wachsm. and Spr. Revision i, p. 85. AValdron, 



Ind. 

 Syn. Macrostylocrinus fasciatus Hall. lb. (2d edit.), p. 130. 

 1852. Macrostylocr. ornatus Hall (Type of the genus). Paleont., New York, ii, p. 



204, PI. 46, figs. 4 a-g. Niagara gr. Lockport, N. Y. 

 1863. Macrostylocr. Striatus Hall. Trans. Albany Inst., iv, p. 207; also 20th Rep. 



New York St. Cab. Nat. Hist., 1867, p. 327, PI. 10, fig. 7. Niagara gr. 



Waldron, Ind., and Racine, Wis. 



