DESCRIPTIONS OF THE SPECIES. 286 



of the hydrospires with the exterior is through the ten linear spiracles (PL XI. 

 fig. 9; PL XV. fig. 11). On the other hand, two of the Belgian Bpecies of Oropho- 

 criiins (0. Orbignyanus and 0. Puzos) have relatively wide radial sinuses, which are 

 incompletely filled by the ambulacra, and portions of the uppermost hydrospire-slita 

 are often visible at their sides, just as in Phamoschisma, from which this genus 

 differs in the appearance of the deltoid plates externally (PI. XIV. figs. 14-18). 

 This character, together with the presence of hydrospires in the anal interradius, 

 also separates Orophqcrinus from Codaster, with which it was compared some years 

 ago by Messrs. Meek and Worthen in the following terms 1 : — "Compared with 

 Codaster, our genus 2 is found to differ in having only two of the slits mentioned in 

 each interradial area, instead of from eight to sixteen, and in having these openings 

 equally developed in the anal as well as in the interradial areas. The internal 

 calcareous compressed tubes are also placed under the so-called pseudambulacral 

 areas as in Pentremites, instead of occupying the whole interradial areas as in 

 Codaster. It therefore seems to be an intermediate type between Codaster and 

 Pentremites, but more nearly allied to the latter than to the former." The above 

 passage shows that the American authors regarded the linear spiracles of Oropho- 

 crinus stelliformis (PL XV. fig. 11) as representing not merely the so-called " ovarian 

 pores " of Pentremites, as they had correctly pointed out already, but also the indi- 

 vidual hydrospire-slits of Codaster, of which there may be eight on each side of an 

 ambulacrum. As a matter of fact, however, the linear spiracles of Orophocritms 

 are not single hydrospire-slits, but the remains of a radial sinus which is elsewhere 

 closed, and corresponds to the whole space between two of the oral crests of Codaster 

 (PL XII. figs. 1-6). The numerous transitional forms between the two genera have 

 been fully described on pp. 88-91, and it is therefore not necessary to discuss the 

 subject again. 



Orophocrinus stelliformis was one of the types employed by the late Mr. Billings 3 

 (under the name of Codonites) in his attempt to demonstrate the fundamental 

 identity of the hydrospire-apparatus of Cystids and Blastoids with the water-vascular 

 system of recent Echinoderms. " The ambulacral canals of the true Crinoids and of 

 the Starfishes are represented in a rudimentary condition in this species by the 

 hydrospires, which open out to the surface through the ten fissure-like spiracles." 

 He made an ingenious attempt to compare the type with Actinocrinus and with 

 the Bipinnaria-larva of a starfish, regarding it as an instance of " the Occurrence of 

 Embryonic Forms among the Palaeozoic Echinoderms." But as his views rested 

 chiefly upon the supposed fact that the mouth is merely an "ambulacral opening," 

 and that the anus is really oro-anal in function, they need not be further discussed. 



1 Report Geol. Survey Illinois, 1873, vol. v. p. 463. 



2 i. e. Codonites, M. & V?., = Oroj)lwcrinus, von Seebach. 



3 American Journ. Sci. 1870, vol. 1. p. 234 ; Ann. & Mag. Nat. Hist. 1871, vol. vii. p. 151. 



