42 UINTACRINUS: ITS STRUCTURE AND RELATIOI^S. 



the flatteniDg, it must have been at least 7 mm. in diameter where it 

 emerged from the disk. The dark tip, shghtlj twisted, is very distinct. 



In No. 150 (PL v.. Fig. 8) the removal of three arms has exposed the 

 anal tube, but none of the disk. The tube is 12 mm. high, and 12 mm. wide 

 at the base ; it rises to about the height of the 25th IIBr. 



In No. 30 (PI. IV., Fig. 5) the tube is shown in a singular position, but 

 one which is readily understood if we bear in mind the method of fossiliza- 

 tion as I have described it above. Here the compression was between lat- 

 eral and vertical, and the disk, instead of being forced upward between the 

 arms, as in No. 148, was pushed downward, and thus cauglit between 

 the walls of the calyx in the concavo-convex position they took in settling 

 into the mud. Some plates of the lower (now outer) side of the calyx being 

 removed, the tube and part of the disk are now seen flattened against 

 the opposite w\all. Several cases of this kind have been observed. In 

 this specimen the black carbonaceous lining beneath the calyx plates is 

 exposed. 



Mouth and Ambulacra. 



The mouth is excentric, and the ambulacra diverge from a point near 

 the margin of the disk. Two of them follow around the margin in a large 

 horseshoe curve, enclosing the anal tube. These branch on either side so 

 as to connect with the arms of the posterior rays. The next pair of ambu- 

 lacra are shorter ; they branch and supply the two lateral rays. A single 

 groove runs to one branch of the anterior ray, and the other branch does 

 not seem to have any groove leading to it. This is the arrangement of 

 ambulacra in specimen No. 75 (PI. IV., Fig. 1), which shows them the plainest. 

 It is very similar in No. 71 (PI. IV., Fig. 2). 



and 1885 (ibid. Pt. III., p. 12) we showed that the arms fundamentally begin with the second plate of the 

 ray, i. e. that all plates of the ray above the "first" radials, whether free or not, are "brachials," it logically 

 followed that they ought to be designated according to their numerical succession. We, in fact, proposed to 

 use the terms "primary," "secondary," and "tertiary" brachials, etc. Upon conference with P. H. Car- 

 penter, who thought these terms too long and cumbrous, we agreed to use "costals," " distichals," and 

 "palmars," as proposed by him. (Ann. and Mag. Nat. Hist., Ser. 6, Vol. YI., pp. 11-18 • Proc. Acad. Nat. 

 Sci. Phil., Oct., 1890, pp. 374-5.) 



In the Monograph we retained, in an explanatory sense, the alternative terms, "primary brachials," 

 "secondary brachials," "tertiary brachials," followed by "brachials of the fourth order," and so on and 

 employed for these the symbols I., II., III., IV., &c. (Mon. Crin. Cam., pp. 73-75). Bather's invention of 

 the terms "prnnibrachs," " secundibrachs," etc., and the other terms naturally accompanying them, with their 

 convenient symbols, was a solution of the difficulties, and gave us a terminology for these parts of the Crinoid 

 skeleton at once so consistent, convenient in use, and easy of remembrance, that I atn sure it must win 

 acceptance by all who will take the trouble to understand it. 



