i62 INVERTEBRATE PALAEONTOLOGY 



Dicyclic Crinoids, in spite of their longer range and 

 later specialization, show comparable diversity in the 

 Upper Palaeozoic. Inadunata are especially abundant. 

 Cupressocrinus, with simple, curiously massive, arms, 

 is one of the most characteristic Devonian Crinoids. 

 Cyathocrinus survived from the Silurian ; while Poterio- 

 crinus, Graphiocrinus and Woodocrinus represented in 

 the Carboniferous the most prolific suborder (Dendro- 

 crinoida) of the Mesozoic. Flexibilia were not yet 

 abundant, but the small Mespilocrinus occurs in the 

 Carboniferous Limestone. Dicyclic Camerates are few, 

 but such as they are correspond with their Monocyclic 

 equivalents in range. Rhodocrinus and Gilbertsocrinus 

 are the most familiar Carboniferous genera. The latter 

 is remarkable in possessing hollow, branched extensions, 

 of unknown function, from the tegmen, between which 

 arise the slender, pinnulate arms. 



The only noteworthy feature in the scanty Holo- 

 thurian fauna of the Upper Palaeozoic is the occurrence 

 of true Synaptidae (indicated by characteristic " wheel " 

 spicules) in the Permian. Stelleroids are not much 

 more satisfactory than those of the earlier era. 

 Bundenbach is a classic locality for Devonian forms, 

 which occur as petrifactions in pyrites, readily cleared 

 from the surrounding slate. Onychaster is a curious 

 Ophiuroid from the Carboniferous. 



Upper Palaeozoic Echinoidea belong to the peculiar 

 group sometimes called " Perischoechinoidea." Unlike 

 all later types, they have more than two columns of 

 interambulacral plates, and many possess extreme 

 ambulacral multiplicity. The tests were commonly 

 ellipsoidal in form ; and the coronal plates, though often 

 massive, were imbricate in arrangement, giving flexibility 

 comparable with that shown by the aberrant Echino- 

 thuriidae of later times. Two main trends of morpho- 



