84 



GEOLOGY 



diminution of the calyx, and a remarkable extension and subdivision 

 of the arms (Fig. 360, d). Unattached crinoids were present. The 



Fig. 360. — Jurassic Ccelenterata and Echinodermata : a, b, Thamnastrcea pro- 

 lifera Becker, a complete corallum, and the lateral surface of a costal septum 

 enlarged; c, Thecosmilia trichotoma (Goldf.); d, Pentacrinus briareus Mill; e, 

 Cidaris coronata Goldf. 



majority of the Jurassic crinoids were undoubtedly shallow- water 

 forms, as most of the Paleozoic types had been; but there is evidence 



