THE ECHINOIDEA 313 



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

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

 & Slad. 



FAMILY 2. TRIPLECHIXIDAE. Echinina in which the ambulacral 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) ; Stirechinus, Desor; Glyptecliinus, Lor.; 

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

 Verrill ; Pedinopsis, Cott. 



Fin. XXXII. 

 Temnoph'tirii.s torctiiii<'.ti<:t!.< (after A.^rassix), showing tlie pitted test. 



FAMILY 3. STRONGYLOCENTROTIDAE. Echinina with more than three 

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

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

 strephus, A. Ag. ; Eurypneustes, Duncan & Sladen ; Pseudoboletia, Trosch. ; 

 Acolopneustes, 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 Colobocentrotus, 

 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. 



