248 



ECHINODERMATA ECHINOZOA 



SUB-BRANCH III 



SECTION D. APETALA. 



Ambulacra flush, apetalous, generally uniporous, and either similar or diverse ; 

 plates high, few, often hexagonal. Fascioles usually present. 



Under this head are included the following recent genera, all but the first 



two of which have fascicles : 

 Genicopatagus, Palaeobrissus, 

 A. Ag. ; Aceste, Wyv. Thom- 

 son ; Aerope, Norman ; Pdlaeo- 

 tropus, Lov6n ; Homolampas, 

 Argopatagus, A. Ag. ; and 

 Cleistechinus, de Loriol. 

 Miocene. 



Family 3. Leskiidae. Gray. 



Test thin, ovoid. Apical 

 system with three basal plates 

 fused into one. Peristome 

 eccentric in front, pentagonal, 

 with five angular buccal plates. 



Palaeostoma, Lov6n 

 (Leskia, Gray). Eecent ; 

 China, East Indian Islands. 



Family 4. Pourtalesiidae. 



Loven. 



Test very elongate, sub- 

 cylindrical or obconical, truncated 

 anteriorly, fiat actinally. Peri- 

 stome in a deep anterior recess ; 

 periproct actinal, or above the 

 projecting posterior rostrum 

 when such is present. Ambu- 

 lacra flush, apetalous, sometimes 

 discontinuous; pores single or 

 slit-like. 



Eecent. 



Mdcropneustes MenegMnii, Desor. 

 Vicenza. 



FIG. 402 bis. 



Eocene ; Monte Spiado, near 



Pourtalesia, Spatagocystis, Echinocrepis, A. Ag. 



Range and Distribution of the Echinoidea. 



Fossil Sea-Urchins make their appearance as early as the Ordovician, but 

 are represented very sparsely by forms differing in a marked degree from the 

 normal (Bothrioddaris, Echinocystites). The order Perischoechinoida, character- 

 ised by its supernumerary columns of plates, is widely, but by no means 

 numerously, distributed in the Devonian and Carboniferous of North America 

 and Europe. 



Fragmentary remains of true Cidarids are found in the Permian, perhaps 



