744 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



in the tjiDical section of the Camerata between the Melocrinidag and Bato- 

 crinidse. In both cases the group with pentagonal base, and in which the 

 anal is unrepresented, is the earliest in geological sequence. 



The Hexacrinidge have not been discovered in any formation older than 

 the Devonian ; but there they occur abundantly in the Eifel limestones, 

 from which twenty-four species have been described. They range through 

 the diiierent divisions of the Subcarboniferous, and are represented in the 

 last member of that system, the Kaskaskia group, by twelve species. Beyond 

 that they are not known ; but we shall not be surprised to hear of a Hexa- 

 crinoid being found in the Carboniferous. 



The Hexacrinidse are the only Camerata in which the arms are uniserial 

 throughout the Devonian ; they gradually become biserial in the Subcarbo- 

 niferous, in the lower part of which all gradations, from nniserial to strictly 

 biserial, are found together in the same genus. 



The family consists of six genera and eighty-five species : fifty -two from 

 America, and thirty-three from Europe. 



HEXACRINUS Austin. 



1843. Austin ; Monogr. Kec. and Foss. Criiioids, p. 48. 



1853. DeKoninck aud Le Hon ; Recher. Crin. Garb. Belg. p. 160. 



1855. F. Roemek; Lethaia Geog. (Ausg. 3), p. 244. 



1857. JoH. MiJLLEE; Neue Echinod. Eifl. Kalk., p. 247. 



1857. PiCTET ; Traite de Paleont., Vol. IV., p. 332. 



1863. DcjARDiN and Hupe; Hist, natur. des Zoophytes Echinod., p. 155. 



1867. Schdltze; Monogr. Echinod. Eifl. Kalk., p. 71. 



1879. W. and Sp. ; Proceed. Acad. Nat. Sol. Phila., p. 252. 



1881. W. and Sp. ; Revision Paljeocr., II., p. 79. 



1831. W. and Sp. ; Revision Palseocr., III., p. 116 (Proceed. Acad. Nat. Sci. Plula., p. 33S). 



Sju. Plati/crimis — PniLLiPS, 1841 (not 1836) ; Palffioz. Foss. Comw., p. 28. 



Syn. Plati/criiius — Goldeuss (iu part) ; 1838, Nova Acta Ac. Leopold. XIX., p. 343. 



Sjn. Plati/crims — Asissiz (in part) ; 1835, Mem. Soc. Neuchat. I., p. 197. 



Sjn. FWymnus — Austin (in part) ; 1842, Ann. and Mag. Nat. Hist., Vol. X., p. 109. 



Sjn. Flatycritms — C. F. Roemeb ; 1843, Versteiu des Havzgebirges, p. 9. 



Syn. Platt/crims — F. A. Roemek; 1844, Rheinish. Uebergangsgebirge, p. 63. 



Syu. Platycrirms — Y. A. Roemeb,; 1851, Verhandl. naturh. Vcrcins f. Rheinlande, p. 362. 



Syn. Plati/mnus — 'L\0'!i; 1860, Trans. Amer. Philos. Soc., Vol. XIII., p. 459. 



The dorsal cup composed almost exclusively of basals and radials ; the 

 latter enclosing a large anal plate. The basals consist of three subequal 

 pieces, forming together a rather large, more or less deep cup or basin, 

 hexagonal in outline. Kadials large, subquadrangular; their superior faces 

 excavated so as to form a facet for the reception of the costals ; the limbs 

 slightly truncated to receive the first row of interradials. The intervening 



