PAL.EOCRINOIDEA. 



435 



genus forms a connecting-link between the Heterocri?iidce and the 

 Cyathocri?iidcz. 



Family 16. Cyathocrinidce. — In this important family of Crinoids, 

 the calyx is irregular, and is of the " dicyclic " type, consisting of five 

 underbasals (fig. 308, b), five basals (/), five primary radials (r), and 

 from one to three anal interradials (a). The ventral surface of the 

 calyx is mainly formed by the large interradial plates, between which 

 are the ambulacral grooves, roofed over with small calcareous plates 



(fig. 297). 



The arms are uniserial, long, 



repeatedly bifurcated 



Fig. 308. — A, Diagram, showing the dissected calyx of Baryprimis (after Hall) : b, Under- 

 basals ; p, Basals; r, Lowest of the three radials ("primary radials"); a. Anal plate. B, Calyx 

 and part of the arms of Cyathocrinus planus, of the natural size. Carboniferous. 



(fig. 309), and without true pinnules. The family of the Cyatho- 

 crinidce. is closely allied to that of the Poteriocrinidce, but the arm- 

 joints are differently articulated in the two, and the arms are repeat- 

 edly bifurcated in the former group ; whereas in the latter the arms 

 may remain simple after the first bifurcation, or branch irregularly, 

 and they, further, carry pinnules. The range of the Cyathocrinidce in 

 time is from the Silurian to the Permian inclusive. 



The principal genus in this family is Cyathocrinus itself (fig. 309), 

 which ranges from the Silurian to the Permian, but attains its maximum 

 development in the Carboniferous Limestone. In this genus the calyx 

 is small and basin-shaped, with long, frequently divided arms. The 

 ventral side is slightly convex, and a plated anal tube is present. The 

 column is round, and is composed of very narrow articulations, which 

 are perforated by a five-angled neurovascular canal. Barycrinns, of 

 the Carboniferous rocks of North America, is nearly related in most 

 respects to Cyathocri?ius ; while Dendrocj'inus (Ordovician), Carabo- 





