202 PROCEEDINGS OF THE ACADEMY OF [1881. 



of them in connection witli the ambulacral system. He showed 

 how impossible it was that the ambulacral canals in some Paleo- 

 zoic Crinoids coukl be continued along the outer surface of the 

 vault, and he reached the conclusion that they passed into the 

 body at the arm bases. It is remarkable that Billings, after mak- 

 ing this important discovery, in connection with which analogy 

 suggested that the food entered the bod}' in the same manner, 

 clung as late as 1810 to the old theory that the subcentral passage 

 in these crinoids — interradiately situated as we have shown — 

 served both as mouth and vent. This view was advocated b3'him 

 in a series of interesting articles, published 1869-tO in tlie Am. 

 Jour. Science and Arts, Nos. 142, 145, 149, as '' Notes on the 

 Structure of Crinoidea, Cystidea and Blastoidea." Since that 

 time, it has been most generally conceded that the interradial 

 opening was the anus onl}', and that the oral centre or mouth in 

 the earlier crinoids was hidden from view by external structures.^ 

 Billings' views with regard to the ambulacral passages were con- 

 firmed by Wachsmuth's discovery of radiating tubes beneath the 

 vault,^ which, as he ascertained, connect with the ambulacral 

 furrows in the arms. We have since examined these tubes in 

 several other specimens, both of Actinocrinus and Strotocrinus, 

 and are enabled to give additional information regarding them. 



The radiating tubes are attached to the vault, running parallel 

 to its inner surface. They consist of five main trunks, which 

 follow the direction of the five main avenues which separate the 

 interpalmar fields. They bifurcate in the same waj^ and until a 

 branch connects with every arm. They are composed of four 

 rows of plates, two below and two above. The two latter touch 

 with their edges the inner surface of the vault, are alternately 

 arranged, and grooved along their median line, leaving a tun- 

 neled passage between the walls of the tube and the vault. The 

 trunks of the two lateral sets of tubes on the same side not un- 



1 The following writers have expressed this opinion : Schultze, 1866, 

 Monog-. Echin. Eifl. Kalk, p. 7 ; Meek and Wortlien, 1869, Proc. Acad. 

 Nat. Sci., Phila., p. 323 ; Loven, on Hypomene Sarsi, reprinted Ann. and 

 Mag. Nat. Hist., Sept., 1869 ; Wachsmuth, "On the Internal and External 

 Stnicture of Paleozoic Crinoids," Am. Jour. Sci. and Arts, Aug. 1877, p. 

 115; Zittel, 1879, Handb. d. Palseontologie. 



^ Described by Meek and Wortben, Geol. Rep. 111., vol. v, p. 329, and 

 Wachsmuth, Am. Jour. Sci., Aug., 1877, p. 119. 



