THE ECHINOIDEA 313 



copsis, Doderlein ; Mespilia, Desor ; Microcyphus, Ag. ; Amblypncustes, 

 Ag. ; Goniopneustes, Dune. ; (?) Holopneustes, Ag. ; (?) Grammechinus, Dune. 

 & Slad. 



FAMILY 2. TRIPLECHINIDAE. Echinina in which the arabulacral plates 

 consist of two primaries and an intermediate demi-plate. The three pairs 

 of pores are arranged in arcs of triplets ; the sutural faces of all plates 

 are smooth ; and there are no pits or grooves in their substance ; so that 

 in these three respects the Triplechinidae differ from the Temnopleuridae, 

 though an approach to this family is shown by Grammechinus. Genera 

 Echinus, Linn. ; Psammechinus, Ag. ; Micropsina, Cott. ; Leiopedina, Cott. ; 

 Tripneustes, Ag. ( = Hipponoe) ; StirechinitA, Desor ; Glyptechinns, Lor. ; 

 Hybechinus, Desor ; Toxopneustes, A. Ag. ; Boletia, Desor ; Evechinus, 

 Verrill ; Pedinopsis, Cott. . 



Fio. XXXII. 

 Temnopleurus tweumaticus (after Agassiz), showing the pitted test. 



FAMILY 3. STRONGYLOCENTROTIDAE. Echinina with more than three 

 constituents in each ambulacral plate, the pores being in high curved 

 arcs. Genera Strongylocentrotus, Brandt ; Sphaerechinus, Desor ; Echino- 

 strephuSj A. Ag. ; Eurypneustes, Duncan & Sladen ; Pseudobolctia, Trosch. ; 

 Aeolopneustes, Dune. & Slad. 



FAMILY 4. ECHINOMETRIDAE. Echinina with three or more con- 

 stituents in each ambulacral plate. The test is elongate, and the long 

 axis does not coincide with the antero-posterior axis. Genera Echino- 

 metra. Gray; Stomopneustes, Ag. ; Heterocentrotus and Colobocentrotiis, 

 Brandt ; Parasalenia, A. Ag. The elliptical shape of the test is the most 

 remarkable character in this family. The perignathic girdle is very 

 powerful, each arch being surmounted by a cap (Fig. XIII. 4). The 

 spines are large and very varied in form. In Heterocentrotus the 

 secondary spines form a fur below the primary spines (Fig. XXXIII.) ; 

 in Colobocentrotus the spines are stout and end in flat surfaces ; they 

 are so crowded together as to form a natural armour-plate (Fig. 



