INVERTEBRATES. 175 



wanting, can be seen nearly as well as in a living Crinoid. It is evidently 

 closely related to P. discoideus of Owen and Shumard (Owen's Report Wiscon- 

 sin, Iowa and Minnesota, p. 588, pi. 5 A, fig. la, lb), with which Dr. Shumard 

 thinks it may be identical; but as neither the specimen described by Prof. Hall, 

 nor that figured by us, shows any traces of the peculiar ridges and other sculp- 

 turing seen on the first radial pieces of P. discoideus, we think these forms 

 specifically distinct. 



Locality and position : Burlington, Iowa; Burlington limestone, of Lower 

 Carboniferous series. 



Genus CYATHOCRINUS, Miller. 



Synon. — Encrinus (sp.), Uee, 1193. History of Rutherglen ; (not of others). 



Encrinites (sp.), Schlot, 1813. Jabrb, 91-89; Petrefact., 1820; (not Miller 

 and others.) 



Cyathocrinites, Miller, 1821. Nat. Hist. Crinoidea, p 85 ; Quenst., 1835, 

 Wegm. Arch., p. 11, 89. 



Cyathocrinus, Agassiz, 1834. Mem. Soc, Sc. Nat. Neuch., ii, and others. 



Pachycrinites, Bchwald, 1840. Bull, St. Petersb. vii, p. 78. 



? Eupachycrinus, Meek and Worthen, 1865. Proeeed. Acad. Nat. Sci. Phila- 

 delphia, p. 159. 

 Generic formula. — 



Basal plates, 5. 



Subradials, 5. 



Radials, 3-|-5, the first large and the others small. 



Anal pieces, 2 or 3. 



The base in this genus is composed of five pieces, which are 

 generally of equal size and form, and united so as usually to 

 present a pentagonal outline. Subradial plates five, alterna- 

 ting with the basal pieces; four of them more or less distinctly 

 hexagonal, and one heptagonal, the latter being generally trun- 

 cated above for the reception of the first anal piece, and some- 

 times supporting on its right superior sloping side, a subanal 

 piece intercalated between it and one of the first radials. 

 First radial plates large, truncated and more or less sinuous 

 above, for the reception of the second radials, usually all alter- 

 nating with the subradials. Second and third radials small, the 

 third being pentagonal or subtrigonal, and supporting the arms. 

 First true anal plate resting upon the truncated upper side of 

 one of the subradials, and inserted between two of the first 



