136 ECHINOIDEA. I. 



Psammechinus Ag. (emend.) 



(Synonyms: Lyt echinus Ag., PsUeckmus Ltk., Scliizcchinus Pomel.) 



Pores trigeminate; primary tubercle on all the ambulacral plates. Slits of the test rather deep. 

 The buccal membrane with numerous plates forming a more or less distinct plate-covering. In the 

 globiferous pedicellarise the blade is not much lengthened. The spicules dumb-bell-shaped, form no 

 border round the globiferous pedicellarise. The spicules of the tube feet bihamate, not branched. The 

 spines of a middle length, greenish. 



Species: Psammech. variegatus (Lamk.), semitubcrciilaitis (Val), verruculatus Ltk. 



Distribution: The eastern and western coasts of tropical America; the Indian Ocean. Lit- 

 toral forms. 



Gymnechinus n. g. 



Pores trigeminate; primary tubercle on all the ambulacral plates. Slits of the test small. The 

 buccal membrane, with the exception of the buccal plates, contains no fenestrated plates at all. In- 

 most in the edge of the mouth more or fewer irregular, needle-shaped spicules are found; also numer- 

 ous bihamate spicules are found, especially nearest to the edge of the mouth and the outer edge. In 

 the globiferous pedicellarise the blade is not much lengthened. The spicules of the globiferous pedi- 

 cellarise arcuate or slightly dumb-bell-shaped, form no border. Smaller, short-spined forms. 



Species: Gymncch. Robillardi (Loriol), darnlcyensis (Woods) 1 ). 



Distribution: Mauritius, Australia. Littoral forms. 

 Toxopneustes Ag. (emend.). 

 (Synonym: Boletia Desor.) 



Pores trigeminate; primary tubercle only on every other ambulacral plate. Slits of the test 

 deep. The buccal membrane with numerous fenestrated plates most of which are quite imbedded 

 in the skin. In the globiferous pedicellarise the blade is much lengthened. The spicules in the globi- 

 ferous pedicellarise are typically dumb-bell-shaped and form a thick, white border round the oiiter 

 edge of the valves; in the tube feet branched, bihamate spicules are found. Large, flat, short- 

 spined forms. 



Species: T. pilcolus (Lamk.), roseus Ag., elegans Doderl. 



Distribution: The Indo- Pacific Ocean. Littoral forms. 

 Tripneustes Ag. (emend.) 

 (Synonym: Hipponoe Gray.) 



Pores trigeminate; primary tiibercle only on ever}- third or fourth ambulacral plate. The pore 

 areas very broad, so that the pores form three separated vertical series; in the small individuals the 

 pores are placed in the usual manner in short arcs. The buccal membrane with numerous fenestrated 

 plates most of which are quite imbedded in the skin. Slits of the test rather deep. In the globiferous 

 pedicellariae the blade is not much lengthened; the pedicellariee upon the whole small and darkly 

 pigmented. The spicules in the globiferous pedicellarise are typically dumb-bell-shaped; they 

 form no border. The bihamate spicules in the tube feet are not branched. Large, high, short- 

 spined forms. 



!) Comp. above p. HO. 



