1869.] BILLINGS — STRUCTURE OP CRINOIDS, ETC. 281 



respiratory areas is the same (in general plan) as that of the 

 genera Glyptocystites, Pleurocystifes and Eckinoencrinites, as will 

 be shown further on. The arms are also arranged in three groups, 

 as in Sphoeronites and Hemicosmites, while the mouth is valvular. 

 On the other hand, the long cylindrical column, and the arrange- 

 ment of the arms around the margin, with the ambulacral pores 

 at their bases, are crinoidal characters. 



In addition to the above, the following species may be referred 

 to, as examples of Crinoids, with the mouth separate from the 

 centre of the radial system. 



Amphoracrinus tesselatus (Phillips). — Figured by J. Rofe, 

 Esq., Geol. Mag., vol. ii, p. 8, f. 3. The figure represents a cast 

 of the interior of the vault, showing the five ambulacral grooves 

 in relief. The mouth is situated in the angle between the two 

 anterior grooves. 



Strotocrinus perimibrosus (Hall, sp.). — Figured by Meek and 

 Worthen, in the Geology of Illinois, vol. ii, p. 188, £ 5. The 

 specimen is 13 lines in diameter, the ambulacral centre 13 lines 

 from the anterior margin, and the mouth 11 lines.* 



Glyptocrinus armosus (McChesney sp.). — This extraordinary 

 Crinoid is figured by McChesney in his " New Pal. Foss.," pi. 7, 

 f. 6, and also by Prof. Hall, in the 20th Reg. Ilep.,N.Y., pi, 10, 

 f. 11, The specimens are between 2 and 3 inches in length. 

 There are ten arms, the anterior side is much inflated, the pro- 

 boscis appears to be large at its base, and eccentric in its position ; 

 but instead of standing erect, it bends down to the surface of the 

 vault, and lies upon it, crossing over to the posterior margin. 

 Judging from the figures, the centre of the base of this organ 

 must be distant from the radial centre at least one-fourth of the 



* In April last I received from Messrs. Meek and Worthen a paper 

 entitled, " Notes on some points in the structure and habits of the Palee- 

 ozoic Crinoidea." Of all the papers relating to this subject yet published 

 on this continent, this one, at least, so it appears to me, is the most 

 interesting and important. It is written with a clearness and particu 

 larity rarely to be seen in palfeoutological memoirs. In some respects 

 it confirms the opinions advocated in these notes, but bears directly 

 against my views on the question here under discussion, i e. — " the 

 position of the mouth with relation to the radial centre." As I wish to 

 give the remarkable observations of the authors full consideration, I 

 shall not discuss them now, but delay until the September J^o. of this 

 Journal. I shall only state here, that I believe that the grooves on the 

 ventral disc of Cyathocrinus, and also the internal " convoluted plate" of 



YoL. lY. T No. 3. 



