694 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Semar/iS. — This species is apparently a descendant of P. sculptus ; its 

 arms, however, are distinct enough for specific separation. It approaches 

 Eucladocrinus in the bifurcation of the arms, but the brachials from which 

 the arms are given off to one half the length of the free rays are not formed 

 into rigid tubes, but retain the character of arm plates. 



Platycrinus Saflfordi Hall. 

 Flate LXVII. Figs. 1, 2, 3. 



1858. Hall; Geol. Rep. Iowa, Vol. I., Part II., ]). 635, Plate. 18, Pigs. 5 and 6. 

 1881. W. aud Sp. ; Revision, Part II., p. 74 (Proceed. Acad. Nat. Sci. Plila., p. 248). 



A large species. Calyx oblong, unusually large in proportion to the 

 arms. Dorsal cup urn-shaped, the bottom broadl}' truncated, the sides 

 gradually spreading to the basi-radial suture, and almost cylindrical along 

 the radials. Ornamentation of the plates as in the two preceding species, 

 but generally somewhat coarser upon the basals, while le.ss distinct at the 

 upper portions of the radials. 



Basal cup large and very deep, its height almost equal to three fourths 

 the length of the radials; the bottom broadly truncated, almost flat; the 

 lower edge sharp, with an undulated outline. Eadials subquadrangular, 

 and in large specimens nearly once and a half as long as wide ; the n\id- 

 dle portions a little elevated, especially toward the facets, the upper angles 

 slightly inflected, leaving a shallow angular depression at the suture line ; 

 the sides of the plates parallel. Facets small, restricted to the extreme 

 upper end of the plates, and occupying but one third of their width. Dis- 

 tichals and the plates of the higher orders to the uppermost axillary moder- 

 ately long, the first plate of each order narrower than the second, and 

 all free from the costals up. Arms short and of moderate size, given off 

 alternately ; biserial from the second plate succeeding the axillaries ; there 

 are from four to six arms in each subdivision, or as many as twelve to 

 the ray. 



Ventral disk depressed hemispherical, the plates more or less convex, 

 covered with numerous small pustules, and each one crowned with two or 

 three conspicuous nodes. Orals very little larger than the adjoining pieces ; 

 the ambulacral plates on the same plane with the interambulacrals. The 

 latter are arranged : 3, 2, 1 ; the middle one of the first row large and hex- 

 angular, that of the anal side a little wider. Anus excentric and directed 



