141 



nearest to the calyx is the last fonnetl one. Fretiueiitly, a certain number 

 of the joints bear root-like extensions, or cirri. The stem and cirri are 

 pierced by an axial canal, round or pentagonal in cross-section. Tlie stem 

 was in most cases attached by a root ( Fig. 29, m-o ). 



Note. — For a more detailed account of the structure of the crinoids, 

 and for a discussion of their development and affinities, see Zittel's 

 "Text-book of Palaeontology" (Eastman's translation), pp. 124-138. 

 The magnificent work of Wachsmuth and Springer, "The Crinoidea 

 Camerata of North America," published by the Museum of Comparative 

 Zoology,* at Cambridge, will be found exhaustive and indispensable to 

 the advanced student of crinoids. 



Specific descriptions are usually scattered through scientific publi- 

 cations ; those of the division Cdinerata. may, however, be found in the 

 monograph of Wachsmuth and Springer, above referred to. 



Genus GENN^OCRINUS. W. and S. 



[Ety. : Gennaiof>, of noble birth; kriiion, lil}'.] 

 (1882: Proc. Acad. Nat. Sci., p. 384.) 



Cah^x deeply indented at the arm region. Plates thin, 

 ornamented with radiating stri;e. Axial canal large, penta- 

 loba-te. Basals three, small. Radials and costals similar, 

 the former five, the latter 2x5. Costals hexagonal and 

 heptagonal, respectively. Above the distichals the branch- 

 ing is from alternate sides, arms branching off at one side, 

 and brachials of a higher order at the other. Arms eight. 

 Interradials nnmerons. Tegmen of small plates; no anal 

 proboscis. 



Genn.^ocrinis NYSSA. (Hall.) (Fig. 28, ci-J.) 



(Actinocrinus nyssn. Hall. 1802. l.")th Rep't N. Y. 

 State (\ab. Nat. Hist., p. 120. ) 



Distinmiishiiw' ClmrHcters. — Calvx wider than hii;li : lobed 

 at arm region; arms given off in clusters; semi-globose 

 cah'x; striated plates, a ridge passing to each face of the 

 plate, and another to each angle; ridges of adjoining plates 

 form triangles; ridges of radial ])lates increase in prom- 

 inence to^^■ards distichals, having at the arm bases almost 

 th(- width of the arms; short Hat basals; radials and costals 

 as long as wide, decreasing rapidly in size npwai'ds; second 



♦Mem. Mus. Comp. Zool., Vol. XXIV. 



