VIII 



EGHINODEBMA TA—S YSTEMA TIG RE VIE W 



299 



EchinasteridSB : AcantJuistcr (numerous arms), Mithrodia, Orihrella, Eddnastcr, 

 Vnlvasicr, etc. Fam. 7. Heliasteridse, with numerous short arms : Seliaster. Fam. 

 8. Pedicellasteridae : Pedicellastcr. Fam. 9. Asteriidae, tube -feet in four rows : 

 Asterias, Uniophora, Coronaster, etc. Fam. 10. Brisingidse, with numerous very 

 long arms, marked off from the small disc : Brisiaga, Labidiaster, etc.'- 



CLASS IV. Ophiuroidea. 



Echinoderniata flattened in the direction of the principal axis of the body, the 

 radii of which are produced into five long, round, simple or nmch branched slender 

 arms. The arms are sharply marked off from the central part of the body, and do 

 not contain either cieca of the intestine or extensions of the genital organs. The 



Fio. 244.— Ophiolepis elegans, LUtken (after Lyman), ds, Dorsal shields ; ss, lateral shields ; 

 etc, dorsocentral ; i&, infi-aba-sal ; &n, basal ; i\i, radial shields ; r, radial. 



axial part of the arms is occupied by a longitudinal row of vertebral ossicles, articu- 

 lated together, and consisting of two fused lateral ambulacral plates or ossicles. 

 The body is usually covered with calcareous plates. On the arms we can distinguish 

 a longitudinal row of ventral shields on the oral side, two longitudinal rows of 



^ The classification of the two orders of the Euasteroidea is that of W. Percy Sladen, 

 Report on the Asteroidea collected hy H.M.S. Challenger. London, 1889. 



