136 



ECHINOIDEA. I. 



Psammechinus Ag. (emend.) 



(Synonyms: Lytcchiiitts Ag., Psilcc/iiiti/x Ltk., Sc/iizrc/ii)iiis Poinel.) 



Pores trigeminate; primary tnbercle on all the ambulacral plate.s. Slits of the test rather deep. 

 The bnccal membrane with nnmeron.s plate.s forming a more or less distinct plate-covering. In the 

 globiferous pedicellariæ the blade is not mncli lengthened. The spicules dunib-bell-shaped, form no 

 border round the globiferons pedicellariæ. The spicnles of the tube feet bihamate, not branched. The 

 spines of a middle length, greenish. 



Species: Psaviviccli. varicgatns (Lamk.), scmitiibcrculatus (Val.), verructilatus Ltk. 



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

 toral forms. 



Gymnechinus n. g. 



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

 buccal membrane, with the exception of the buccal piates, contains no fenestrated piates 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 pedicellariæ the blade is not much lengthened. The spicules of the globiferous pedi- 

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



Species: Gyii/ncc/i. Robillardi (Loriol), daridcyoisis (Woods)'). 



Distribution: Mauritius, Australia. Littoral forms. 

 Toxopneustes Ag. (emend.). 

 (Synonym : Bolrtia Desor.) 



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

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

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

 ferous pedicellariæ are t\-pically dumb-bell-shaped and form a thick, white border roxmd the outer 

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

 spined forms. 



Species: T. pilrolus (Lamk.), roscits Ag., clrgai/s Doderl. 



Distribution: The Indo- Pacific Ocean. Littoral forms. 

 Tripneustes Ag. (emend.) 

 (Synonym: Hipponoc Gray.) 



Pores trigeminate; primary tubercle 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 nmnerous fenestrated 

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

 pedicellariæ the blade is not nurch lengthened ; the jDedicellariæ upon the whole small and darkh' 

 pigmented. The spicules in the globiferous pedicellariæ are typically dumb-bell-shaped; the\' 

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

 spined forms. 



'I Comp. above p. 1 10. 



