340 HAWAIIAN AND OTHER PACIFIC ECHINI. 



to define. Mortensen (1903, "Ingolf " Ech., pt. 1) has made clear the interesting 

 characters shown by the pedicellarise, and although he greatly exaggerates their 

 importance, it is beyond question that they are suggestive and oftentimes useful 

 for systematic purposes. By using them in connection with the structure of 

 the ambulacra, the arrangement of the oculars, the buccal membrane, the thick- 

 ness or thinness of the test, and the primary spines, it is possible to break up the 

 large and heterogeneous genus Strongylocentrotus into smaller and more homo- 

 geneous genera. Mortensen made seven such groups, basing his divisions 

 chiefly on the pedicellarise and spicules, and placing the resulting genera in three 

 different families. His genera are Strongylocentrotus, Paracentrotus, Lox- 

 echinus, Sphserechinus, Pseudocentrotus, Anthocidaris, and Toxocidaris. Of 

 these the first three seem natural groups, and the same is true of the last, though 

 it is necessary to recognize it under another name. As already shown (p. 281), 

 the type of Toxocidaris is Echinus erythrogrammus Val. and the type of Helio- 

 cidaris is Echinus tuberculatus Lamk. As these two species are indubitably 

 congeneric, the later name (Toxocidaris) becomes a synonym of the earlier 

 (Heliocidaris) , and the genus, which Mortensen calls Toxocidaris, and for which 

 he definitely designates erythrogrammus as the type, must be called Heliocidaris. 

 As regards Sphserechinus, it is impracticable to retain the genus, in spite of 

 Mortensen's statement that it is "very well characterized." His definition 

 of the genus as "large, short-spined forms, almost globular," and other references 

 to the "high form" of the test, show that he has not examined large series of 

 specimens. Many of our specimens of Sph. granularis from the Azores are 

 greatly flattened, the vertical diameter scarcely exceeding one half the horizontal, 

 and one specimen, 76 mm. in diameter is less than 37 mm. high. Many of 

 these specimens also have somewhat longer spines than usual, and except for 

 the deep gill-cuts and the insert oculars, would be easily mistaken for Paracen- 

 trotus limdus from the same islands. In the number of pore-pairs in an arc 

 these specimens of granularis from the Azores, show great diversity, many arcs 

 having as many as seven pairs, and six seems to be the typical number for adults. 

 The deep narrow gill-cuts furnish a good specific character and one that is 

 remarkably constant, but unfortunately it does not make a useful generic charac- 

 ter, for it occurs nearty or quite as well developed in many specimens of S. 

 depressus and S. pulcherrimus, but in these species, is very variable and of little 

 significance. The species hitherto known as " Sphoerechinus " australice proves 

 to have little in common with granularis, except well-defined gill-cuts, and it 

 may best be placed in a genus by itself. It cannot retain the name Sphserechinus 



