NEOCRINOIDEA. 



443 



of the Rosy Feather-star, and there are grounds for believing that 

 their presence is characteristic of the family. They never reach any 

 great size, however, and fuse at an early period with the enlarged 

 top stem-joint or "centrodorsal." The basals are very generally 

 rudimentary, being reduced to a small "rosette-plate," concealed 

 between the centrodorsal and the primary radials. In Atelecrinus 

 and Tkaumatocrinus, however, and in most fossil Comatidce, the 

 basals persist and are visible externally. There are three, or, 

 rarely, two cycles of radials ; and, except in Thaumatocrinus, de- 

 finite calyx-interradials are not developed. There are five or ten 

 arms, which are either simple or more or less divided. A large 

 number of living forms of the " Comatulce " are known, with a 

 very wide range in space. As regards their distribution in time, 

 the earliest types of the Feather-stars are found in the Jurassic 



Fig. 316. — Centrodorsal (cd) and radial pentagon (r) of A ntedon inczin'a, enlarged six times. 

 Cretaceous (Upper Greensand). A, Side-view ; b, View from above ; c, View from below. (After 

 P. H. Carpenter.) 



rocks (Antedon, Actinometra, &c), and there are also various Cre- 

 taceous and Tertiary types. The parts most commonly preserved 

 in a fossil condition are the centrodorsal plate and radial penta- 

 gon (fig. 316); and upon remains of this nature, before their 

 true character was understood, the generic name of Solanocrinns 

 (" Glenotremites") was founded. The names of Allionia, Gany- 

 meda, &c, were also based upon the isolated centrodorsals of 

 fossil Comatulce. 



The extensive genus A?itedo?i possesses a central or subcentral mouth 

 and ten or more arms, while the basals of the recent species form a 

 " rosette," and are invisible externally. The earliest fossil species appear 

 in the Lias. Eudiocri?ins resembles Antedon, but has only five arms. 

 The genus is represented by a single Cretaceous form, but living types 

 are known. Actinometra differs from Antedon in the fact that the 

 mouth is excentric or marginal in position. The genus ranges from the 

 Jurassic period to the present day. Lastly, in the Jurassic and Creta- 

 ceous genus Thiolliericrinus, the centrodorsal plate exhibits a cavity 

 which is usually filled by the first joint of the persistent stem, the lower 



