144 



ridges extending t'roni tlie base to tlie ten arms, along the 

 five rays. 



Found in the Moscow shale of Section 5, two feet above 

 the base (two specimens). 



Note. — This species is the first of the genus noted above 

 the Silurian, as well as the first representative of the genus 

 in America; the other species being known from (lotlaud 

 and England. 



Genus PLATYCRINUS. ]^Iiller. 



[Ety. : Platys, flat ; krinon, lily.] 



(Miller, Natural History of Crinoidea, p. T3, 1821.) 



Calyx composed of three unsymmetrical and freiiuently 

 anchylosed basals, succeeded by five large radials, laterally 

 united by close sutures, their upjier margins crescent-shaped. 

 The costals are small and axillary, the single series being 

 often entirely hidden. The distichals commonly in tworow^s, 

 the upper axillary, and l)earing the ])almars. The first row 

 of interradials is on a level with the arm bases, and is in 

 part interbrachial, and in part interambulacral. The suc- 

 ceeding interradials are all interaml)ulacral. Anal interra- 

 dius of numerous plates. Arms simple, dividing and becom- 

 ing biserial, i. e., composed of a double row of plates. Pro- 

 boscis often present. Stem elli|)tical and twisted, with a 

 minute axial canal. 



Platycrinus eriensis. Hall. (Fig. 2(5.) (loth Rep't 

 N. Y. State Mus. Nat. Hist., p. 119, PI. I.) 



Distinguishin<>- Clmracters.— Small cup-shaped 

 calyx ; comparatively large column facet, bor- 

 dered by a thick rim; anchylosed basals: radi- 

 als wider tlian high, with prominent articulat- 

 FiG. 26. Pkity- unr surface above; first costal quadrangulai-; 



crinus er i e ns is -. 



(after Hall). sccoiid costal axillary, pentagonal : sub-angular 

 arm joints; strong pinnules; granulose plates. 



Found "in the shales of the Hamilton group, near Ham- 

 burgh, Erie County, N. Y." (Hall.) 



