366 HAWAIIAN AND OTHER PACIFIC ECHINI. 



THE SPINES, PEDICELLARI.E, SPH^RIDIA, AND SPICULES. 

 Plate 95, figs. 1-15. 



In no other family do the spines reach such a degree of specialization as they 

 do in the Echinometridse. While Parasalenia and Echinometra are not remark- 

 able in this respect, the remaining genera are extraordinary. In Heterocentro- 

 tus, the primary spines have become so long and stout, as to give the animal a 

 very heavy appearance, while the secondaries, though not lengthened are greatly 

 thickened. In Colobocentrotus and Podophora on the other hand, the spines 

 are all reduced to a uniform length abactinally and being correspondingly thick- 

 ened, they have come to form a close, smooth covering over the whole upper 

 surface. Although little is known of the habits of the species, contained in these 

 three genera, it can hardly be doubted that these remarkable modifications of 

 the spines are due to the conditions under which they live on surf -exposed reefs. 

 Even in Echinometra, a tendency for the abactinal secondary spines to become 

 modified in a manner somewhat similar to that shown by Podophora is found. 



The pedicellariae of the Echinometridse are not sufficiently different from those 

 of the Strongylocentrotidae to warrant any extended description. The valves 

 of the globiferous have as a rule, a single lateral tooth on the left side but this 

 is wanting in Parasalenia and there is considerable diversity, in Podophora, 

 the lateral tooth sometimes occurring on the right side, and occasionally either 

 it or the terminal tooth is paired (see A. Agassiz, 1908, Mem. M. C. Z., XXXIX, 

 PI. 5, figs. 10-13). As a rule, these pedicellariae are smaller than in the Echinidse 

 and Strongylocentrotidse, but in some species they are well developed. The 

 ophicephalous, tridentate, and triphyllous pedicellarise are commonly present 

 in large numbers and reveal great diversities of form, even within a single species. 

 As they have been very fully illustrated for Colobocentrotus and Podophora 

 (A. Agassiz, 1908, 1. c.), it would be quite superfluous to figure or discuss them 

 in detail here. The tridentate in spite of their diversity sometimes furnish 

 excellent specific characters. 



The sphseridia occur as in the related families on the actinal portion of each 

 ambulacrum. There are commonly 4-6 in each area but there may be 8 or 

 even more. They show great diversity in form, as has been very fully shown 

 recently, for Colobocentrotus and Podophora (A. Agassiz, 1908, Mem. M. C. Z., 

 XXXIX, Pis. 31 and 32). 



The calcareous spicules of the pedicels, show an unusual diversity. They are 



