IIOLOTIIUROIDEA. 297 



small tithe feel. Five genital pores in the region of the madreporic 

 plate. 



Faro. Clypeastridse. The edge of the disc without indentations. Cltjpcaster 

 rosaccus Lam. (fly;. 207), Echinocyamus pusillw 0. F. Miiller, Mediterranean. 



Fain. Scutellidae. Flattened EcMnoulca with a shell often lobed or per- 

 forated, with rows of pores for the ambulacral feet. Lolopliora lifora Ag., 

 Rotiiln Jtiinijfhii Klein, Africa. 



Order 3. SPATANGIDEA. 



Irregular Echinoidea of a more or less heart-shaped form, with 

 eccentric mouth and anus. There are no teeth or masticatory apparatus, 

 and there is usually a four-leaved ambulacral rosette and four genital 

 plates. 



As a rule there are semitse and four genital pores, but the number 

 of the latter may be reduced to three and two. 



Fam. Spatangidae. Spatanf/va jmrpurcus O. Fr. Miill., Mediterranean; 

 Schizaster canaliferus Ag., Brissus Klein. 



CLASS IV. HOLOTHUEOIDEA.* 



Wormlike elongated Echinoderms with a leathery body wall, with 

 contractile tentacles surrounding the mouth ; anus terminal. 



The HolotJiuria approach the worms in possessing an elongated 

 cylindrical shape and a bilateral symmetry, which is expressed in 

 many ways. In particular they possess so striking a resemblance, so 

 far as their exterior is concerned, to many Gephyrea that formerly 

 they were included in the same group. The body-covering never 

 consists of a firm calcareous shell like that which we find in other 

 Echinoderms, but always remains soft and leathery, the calcareous 

 matter being confined to a few isolated particles of definite form. 

 In rare cases (Cuvieria), scales are present in the dorsal skin. 

 These are arranged like the slates on a roof, and may even take the 

 form of spicule-like appendages (Echinocucumis). 



The bilateral symmetry results not only from the existence of un- 

 paired organs, but from the contrast which is often very distinctly 

 expressed between the dorsal and ventral surfaces. The ambulacral 

 feet are not in all cases regularly arranged in the five meridional 



* G. J. Jaeger, " De Holothuriis." Dissert, inaug. Turici. 1833. J. F. Brandt. 

 " Prodromus des-criptionis aniinalinm al> TL Mcrtonsio in orbis terrarum 

 circumnavigatione observatorum," Fasc. I. Petropoli, 1835. J. Miillur, " Uebcr 

 Synapta digitata uud iilier die Erzeugung von Schnecken in Holothnrien," 

 Berlin, 1852. A. Baur, " Bcitriigf zur Naturgcschichte der Synapta di'jitata," 

 Dresden, ISiU. C. Semper, " Reisen im Archipel der Philippinen," Tom J., 

 Leipzig, 1868. 



