POTERIOCRINUS. 225 



have been very thin and very intimately united, consequently it is quite impossible 

 to trace the divisions of the upper parts of the calix, which are, moreover, in 

 many of the specimens wanting. Some of the arms are, however, occasionally 

 clearly shown, and a few scattered plates of the dome are seen in one of the 

 specimens. 



The tubercles on the plates of the cup seem to vary very considerably in 

 number and size. They appear to be conical, and higher than wide, and may be 

 in the shape of small spines. 



Affinities. The basal disc is remarkably like that of Arthracantha Ithacensis, 

 Williams, 1 as figured by Wachsmuth and Springer ; 2 but, if it had spines, they were 

 probably very much smaller and more like those of A. punctobrachiata, Hall, sp. 8 

 The ornament of Hexacrinus inter scapularis, Phillips, sp., 4 may also be compared. 



The fossil doubtfully described by Romer 5 as Geriopora ? patina certainly 

 presents much superficial resemblance in general shape to some of our specimens, 

 though the ornament seems closer and more regular. Romer himself notes its 

 likeness to a Crinoid. 



3. ORDER INADUNATA, Wachsmuth and Springer, 1885. 



In the maze of this order it almost requires a necromancer to bring down a 

 species to its rightful place amid the kaleidoscopic genera that appear, change, and 

 vanish with the progress of science. With such obscure data as our Pilton fossils 

 the results must necessarily be highly problematical. 



I. Family POTBRIOCEINID^, Austin, 1850 ? (emend. Wachsmuth and Springer, 



1886). 



1. Genus POTERIOORINUS, /. 8. Miller, 1821. 



Wachsmuth and Springer, 6 finding difficulties in reference to Miller's type 

 species P. crassus, 1 propose P. notabilis, Meek and Worthen, as " a new, or at 



1 1883, H. S. Williams, ' Proceed. Amer. Pbilos. Soc.,' p. 85, plate. 



2 1897, Wachsmuth and Springer, ' N. Amer. Crinoid. Camer.,' vol. ii, p. 749, pi. Ixxvi, figs. 1 ac. 



3 Ibid., p. 750, pi. Ixxvi, figs. 2 a, b. 



* 1895, Whidborne, ' Dev. Fauna,' vol. ii, p. 190, pi. xxi, figs. 1-4, and pi. xxii, figs. 1- 



5 1850, F. A. Komer, ' Beitr. Harzgeb.,' pt. 1, p. 8, pi. ii, figs. 3 a, b. 



6 1879, Wachsmuth and Springer, ' Proc. Acad. Nat. Sci. Pbilad.,' 1879, p. 327. 



7 1821, J. S. Miller, ' Nat. Hist. Crinoid.,' p. 68, pi. xxiii, figs. 117. 



