988 MB. F. A. BATHER OS TTIXTACIlINrS. [Dec. 17, 



more tl i .■ fhe average), we conclude that the total length must be 

 10cm.-| ■&() cm. = 106 cm. Similarly, taking it that the height of 

 a brachial has to decrease from 1*4 mm. to '65 mm. and that the 

 rate of decrease is, at the utmost, -2 mm. in 20 cm., then we 

 conclude that the total length was not less than 10 cm. + 80 cm.= 

 90 cm. This latter method is not quite so reliable as the former, 

 since measurements are more difficult to make, and since svzygies 

 interfere with the striking of a correct average. But we are 

 certainly justified in concluding that in aii adult the length of a 

 free arm-branch, counting from the suture between the eighth and 

 ninth secundibrach, A'sas certainly not less thaii lUO cm., or about 

 3 feet 'dh inches, and that it contained fully 1000 brachials. Con- 

 sequently, to adapt the words of the first describer of this crinoid, 

 " it seems probable that in life the spread of the outstretched arms 

 may have been " 6 feet 9 inches " or more." The longest arms in 

 other crinoids are about 26 cm., or 10^ inches, in Extrucrinus from 

 Boll, and about 22 cm., or a little under 9 inches, in Scaphiocrinvs 

 swallowi from the Carboniferous of jSTorth America. Enormous 

 though the length is, as compared with that attained by other 

 crinoids, the drawing of a reconstructed individual shows that it is 

 by no means excessive when compared with the size of the dorsal 

 cup (Plate LV.). 



The arm-branches are found stretched along ventralwards, or 

 opened at right angles to the cup, or bent back aborally, sometimes 

 straight, sometimes curved, sometimes coiled round in a loop of 

 half an inch or less in diameter. It is clear that they had great 

 power of motion in all directions ; and this is borne out by 

 the structure of the brachials. 



The brachials are usually compressed along different axes, 

 according as they he on the slab, so that it is hard to estimate 

 their exact shape. It appears that the more proximal brachials 

 were wider than deep (PI. LIV. figs. 6, 8), while the more distal 

 ones were deeper than wide (PI. LIV. figs. 2, 5), also that the 

 more distal brachials were higher in proportion than the more 

 proximal ones. Owing to the pinnulatiou, the sutures between 

 the brachials are not parallel, but slope alternately right and left. 

 This feature, which was marked in the fixed brachials, is barely 

 perceptible in the more proximal free brachials, but increases distal- 

 wards. The more proximal brachials are smoothly and regularly 

 rouuded ; but the more distal ones become excavate and develop a 

 clearly marked ridge, or cornice, on their distal margins, which 

 ridge is more intense on the side towards the pinnule (PL LIV. 

 fig. 11). _ 



The ventral groove is V-shaped. In the more proximal brachials 

 it is wide and enclosed by convexly curved sides (PI. LIV. fig. 6) ; 

 in the more distal brachials it becomes gradually deeper and is 

 enclosed by straight sides (PI. LIV. figs. 2, 5). Covering plates to 

 the ventral groove have not been observed ; probably they were 

 small and lay, separate from one another, in a membrane, and so 

 woidd not readily be preserved in situ. 



