SUB-CLASS I ASTEROIDEA—ENCRINASTERLE 207 
Sub-Class 1. ENCRINASTERIAE. Bronn. 
Palaeozoic Star-fishes with but slightly inclined ambulacral ossicles, their ends 
meeting alternately in the middle of 
the ambulacral grooves. Madreporite 
situated on the oral side of the disk. 
Cambrian to Carboniferous. 
Two principal groups may be 
indicated in this sub-class, in one 
of which marginal plates are 
strongly developed, and in the 
other they are either absent or 



rudimentary. So little is known, aug ee 
however, of the complete structure Sy ae : 
of the majority of Palaeozoic forms, aS CES 
that in the case of some genera it ES : 
is impossible as yet to determine ge < 
positively the group in which they Fic. 337. 
should be classed. Aspidosoma petaloides, Simon. Lower Devonian ; vicinity 
of Niederlahnstein, Nassau. A, Ventral aspect, natural size. 
To the first group belong the B, Arm viewed from the dorsal side. C, Ventral aspect of 
following genera :— Aspidosoma, arm, enlarged (after Simonowitsch). 
Goldf. (Fig. 337). Devonian; Rhenish Prussia. Palaeaster, Hall (Petraster, 
Billings; <Archasterias, 
Miiller), (Fig. 338). Ordo- 
vician to Carboniferous ; 
Europe and North America. 
Salteraster, Stiirtz (Palae- 
aster, Salter, p.p.) | Ordo- 
vician ; England. Palaeo- 
stella, Stiirtz. Lower De- 
vonian ; Bundenbach. 
Palasterina, M‘Coy 
(Cambrian to Devonian ; 
Europe and North America), 
should probably be ranked 
in this groupas a transitional 
form. Urasterella, M‘Coy 
(Stenaster, Billings,  p.p.), 
Ree ag! (Ordovician ; Canada), is 
Palaeaster Eucharis, Hall. Devonian; Hamilton, New York. also considered by Stiirtz as 
A, Ventral aspect, natural size. B, Dorsal surface of one of the arms. » Ons ees 
C, Diagrammatic view of ventral surface of the arms (after Hall). a member of this group. 
To the second group 
belong the genera: Palaecocoma, Bdellacoma, and Rhopalocoma, Salter. 
Silurian; England. Loriolaster, Cheiropteraster, and Palasteriscus, Stiirtz. 
Lower Devonian ; Bundenbach. 

