110 lft,0CEEUING8 OF THE ACADEMV Of [1886. 



torily that also the lower plate in the allied genera is under- 

 basal. Myrtillocrinus, in our opinion, is closely allied to Gas- 

 terocoma, if not identical with it, but it is possible that the anal 

 opening which has not been observed was subcentral, in place of 

 lateral. It also appears from Hall's figure, as if it had two arms 

 from each ray , although there is but one axial canal, which occupies 

 the central space of the facet. The facet in Hall's species is oval 

 and strictly lateral, thus indicating that the arms were pendent. 

 Geological Position, etc. Only two species are known, the 

 one from Europe, the other from America, both coming from 

 lower Devonian beds. 



1S62. Myrtillocrinus americanus Hall, 1 Jth Rep. N. York St. Cab. Nat. Hist., p. 

 142, PI. 1, figs. 2-4. Upper Helderberg group. Livingston Co., N. Y. 



1855. M. elongatus Sandberger (type of the genus), Verstein. Nassau's, p. .'588, PI. 

 35, fig. 6. Pictet, Traits de Paleout., iv, p. 311, PI. c. fig. 4. Dujardin and 

 Hupe, 1862, Hist, natur. d. Zooph. Echinod., p. 108. Miiller, 1857, Neue 

 Echin. Eifl. Kalk., p. 257. Devonian. Nassau, Germany. 



b. Branch, FISTULATA, W. and Sp. 



The Fistulata embrace the Cyathocrinidse as they were defined 

 by us heretofore, but which we now subdivide into Hybocrinida?, 

 Heterocrinidse, Anomalocrinidae, Cj^athocrinidse and Poterio- 

 crinidiB. To these we add the Belemnocrinid.ne, Astylocrinidae 

 and Encrinidse. 



Zittel defined his Hybocrinidse as follows : Calyx irregular ; 

 basis monocj^clic ; basals 5 ; radials 5 ; arms slender, single- 

 jointed ; pinnules wanting ; and he placed in the family : Hybo- 

 crinus and Anomalocrinus. His definition is deficient and not 

 quite correct. It would admit Pisocrinus and Rhopalocrinus, 

 which we recognize as members of very different groups ; and it 

 actually excludes Anomalocrinus, which has seven plates in the 

 radial series and not five, and strong pinnules, which are wanting 

 in Hybocrinus. 



Hybocrinus represents a very peculiar form. No other palaeo- 

 zoic Crinoid deserves in so high a degree the designation embry- 

 onic type as this genus, Hybocystites and the allied genera 

 Hoplocrinus and Baerocrinus, which Zittel took to be synonymous 

 with Hybocrinus. These four genera, which are easily recog- 

 nized by their monocyclic base, large body, imperfectly developed 

 radial plates, small ventral sac, the embryonic state of their arms. 



