CRINOIDEA. 65 



Radials separated posteriorly by anal x; RR hexagonal in general outline. Primibrachs 

 2x5, laterally separated by ilBr. IAx often slightly out of vertical alignment. Ar- 

 rangement 1 of brachials above IAx ant. and post. lats. 2IIAx, 4IIIBri, 4IIIBr2, free 

 biserials. Anterolaterals. . .2IIBri, 2IIBr 2 , 2IIBr 3 , free biserials. 



"Arms biserial, branching and gradually diminishing in size upwards;" 2 biserials 

 usually not incorporated, "Pinnules small and rarely preserved." "Ambulacral cover- 

 ing plates biserially arranged and bordered by a series of side plates." 



Interbrachials numerous ilBr, regular in arrangement but not constant in number, 

 the mean being approximately 1, 3, 3, 2, 2, 3, and the size growing progressively smaller 

 from below upwards; ill Br regularly arranged, but with slight variation in number, as 

 for example 1, 2, 1 and 1, 2, 2, I IIIBr few or none, large or small. All interbrachials 

 meeting the interambulacrals. 



Anal x narrower than the radials but of equal height; secondary anals one, rarely 

 more; anal interbrachials of varying number but growing progressively smaller from 

 below upwards and meeting the interambulacrals; anal interray usually broader than 

 the others. 



Tegmen wider than high, convex to conical, or, rarely flattened; anal tube large, 

 excentric; tegmenals numerous not regularly arranged, but growing progressively smaller 

 from center to margin of calyx. "Orals" and radial dome plates often accentuated in 

 size or ornamentation, being larger than the other plates and occasionally spinose or 

 with greater convexity. Ambulacral areas slightly elevated; interambulacrals de- 

 pressed and meeting interbrachials: ambulacral cover plates often distinct marginally 

 and with the "side plates" entering the tegmen. 



"Column circular, large, with strong cirri at distal end; axial canal quinquelobate." 



Range: Devonian. 



To this group the following species may be assigned without question: M. rugosus 

 Lyon and Casseday (Corniferous) ; M. farnsworthi (White), M. depressus (Hall), 

 M. multidecoratus (Barris), M. nodosus (Barris), and the three species to be described 

 later. 



The following species offer some variations: M. latus (Hall) has apparently no 

 anal tube, M. spinosulus Lyon has 8 arm openings to each ray, M . concavus Wachsmuth 

 has very few ilBr, and no illBr or illlBr, while M. abnormis (Lyon) is evidently a col- 

 lection of abnormal individuals oi doubtful generic and specific standing. 



Megistrocrinns broadheadii n. sp. 

 Plate 8, figures 5-7. 



Species large. Calyx nearly as high as wide; deeply invaginated aborally, highly 

 convex orally; basals, radials and lower 1/3 of IBn curving upwards, sides of cup sloping 

 but slightly outward from IBn to arm bases. Radial areas elevated, interradial areas 

 depressed; anal tube slightly excentric, large. 



Basals and radials included in aboral invagination not distinct owing to the peculiar 

 preservation which foils successful cleaning. Primibrachs 2x5; IBri slightly larger than 

 ilBn, IAx offset in the anterior and post-lateral rays, symmetrically placed in the 

 antero-Iateral rays. Brachials above IAx arranged as described in the generic diagnosis. 



>The bind and trifld arrangement of the arms, so well expressed in the Devonian forms 

 of this genus, is not of rare occurrence, being found in varying degrees of expression in many 

 widely separated genera. In Botryocrinus it is shown by the angle of the radial facets in refer- 

 ence to the vertical axis of the calyx; in Mysticocrinus in the lack of IBn and distal radial 

 spines in the ant. -laterals; and in Pisocrinus in the peculiar subequal size of the anterior, 

 and left posterior radials and the right-post, inferradial. 



I have mentioned but three examples of this phenomenon, yet its occurrence is so wide- 

 spread and so clearly delineated that there can be no doubt that there is some fundamental 

 principle governing it, but just what it is I am not ready to state. 



•Statements in quotation marks after "Wachsmuth and Springer, in N. Am. Cam. 

 Crinoidea. p. 532. 



3 



