GENERAL INTRODUCTION TO THE ZOOLOGICAL REPORTS. 



45 



presented by existing genera such as Hyalonema (fig. 15), in beds of the Carboniferous 

 and Silurian periods. Some of the recent species, Euptectella as2:>ergillum (Owen), and 

 Ajjhrocallistes hocagei (Wright), are among the most delicate and beautiful of living 

 organisms ; the genus UmbelMa and several other characteristic Pennatulidse ; several 

 fine new species of the Crinoid genus Pentacrhms, so abundant in the blue clays of the 

 Lias; and species of the genera Rhizoc}'inus (fig. 17), Bathycrimis, and HyocnJius, crinoids 



Fro. il.—Polyckeles crucifer, v. W.-S. 



having few afiinities with familiar living animals, but nearly related to the Apiocriuida3 

 of Jurassic times ; a series of star-fishes related more or less nearly to the genera Archaster, 

 Porcellanaster, and Hymenaster, genera rich in species and recalling many fossil forms ; 

 species of the genera Porocidaris and Salenia ; what turns out to be a large and 

 prominent family of regular urchins, the Echinothuridfe, long known only by an obscure 



