UINTACRINUS: ITS STRUCTURE AI^D RELATIONS. 45 



Amon<T the Palifiozoic Inadunata, so far as known, the mouth is sub- 

 tegminal, and the ambulacra either subtegminal or covered with strong, 

 apparently rigid plates. In the Fistulate division a great develop- 

 ment of the posterior interradius into an elongate ventral sac in 

 many cases tended to push the oral centre to one side, so that in 

 genera like Scaphiocrimis, Scytalocrinus, Decadocrinus, etc., the mouth 

 must have been subcentral or marginal. Whether it remained so in the 

 Mesozoic Encrinidce, in which the ventral sac had almost disappeared, 

 cannot be determined from the material thus far discovered, — although it 

 seems probable, if the structures described by Wagner and von Koenen 

 are correctly interpreted. 



In Holocrinus, from the Triassic, Wagner * found a tegmen of somewhat 

 similar conical form to that of Apiocrinus, composed of circular and elliptical 

 granules and plates, of different sizes. The plates have a well-defined 

 suture, and in the closeness of their connection, Wagner says, closely 

 resemble the tegmen of Apiocrinus described by de Loriol, though in 

 a second specimen found by him {Op. cit. 1891, Taf. XLIX., Figs. 2 a-b) 

 he thinks the tegmen, in its uniform construction of small, round plates, 

 not touching one another, resembles that of Antedon anrjustical)/x or A. ine- 

 qualis (p. 885). It is impossible to tell from Wagner's figures where the 

 anal opening is. P. H. Carpenter {Op. cit. p. 882-3), on examining the speci- 

 mens, was " puzzled by the absence of any indication of ambulacral plates," 

 though he afterward (p. 884) thought that three ambulacra might be repre- 

 sented by Wagner's Fig. 2 b. Profes.sor von Koenen t afterwards made 

 some very interesting observations upon the same specimens of Holocrinus. 

 By removing some of the surrounding matrix he was able to obtain a better 

 view of the structure. On Wagner's first specimen {Op. cit. 1887, Fig. 1, 

 1891, Fig. 2 a) he found in the deep depression lying between the base of 

 the two broken arms and the elevated ventral sac an opening from which 

 run two grooves to two different radii, one of which branches for the two 

 arms. He takes the opening to be the mouth and the grooves to be ambu- 

 lacral furrows. On the side of the conical elevation opposite from the 

 mouth opening he found a second opening, which he thinks may be con- 



* Ueber Encriims Wa(;neri Ben., aus dem uuteren Muschelkalk, von Jena. R. Wagner, Zeitscli. 

 Deutsch. Geol. Gesell., 1887, XXXIX., p. 822 ; 1891, XLIII., pp. 879-887, (4) Taf. XLIX., Figs. 1 

 and 2. 



t Entwicklung von Dadocrinus gracilis v. Buch, und Holocrinus Waffneri Ben., 1895. Naclir. d. K. 

 Gesell. d. Wissensch. zu Goettingen, Heft 3, p. 283. 



