366 HAWAIIAX AND OTHER PACIFIC ECHINI. 



The Spines, Pedicellari^, Sph^ridia, and Spicules. 



Plate 95, figs. 1-13. 



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

 do in the Echinometridaj. 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 upp>er 

 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 bj^ Podophora is found. 



The pedicellariai of the Echinometridae are not sufficiently diflferent from those 

 of ih(^ Strongylocentrotidaj to warrant any extended description. The valves 

 of tlic (jlobifcrous 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. .\gassiz, 1908, Mem. M. C. Z.. XXXIX, 

 PI. 5, figs. W-IS). As a rule, these pedicellaria? are smaller than in the Echinidae 

 nn(i Strongylorentrotidir, but in some species they are well developed. The 

 opliici'phdlou.s, tridcntatc, and triphyllous pedicellaria? are commonly present 

 in large numl)ers and reveal great diversities of form, even witiiin a single species. 

 As they ha\(' been very fully illustrated for Colobocentrotus and Podophora 

 (A. .Xga.ssjz, 19()S, 1. c), it would be quite superfluous to figure or discuss them 

 in detail here, 'i'he triilentate in .spite of their diversity sometimes furnish 

 excellent specific chnrnrters. 



The splueridia occur as in the related families on the actinal i>ortion of each 

 anibulncruni. Thrre Mre conunonly 4-0 in each area but there may l)e 8 or 

 even more. They show great diversity in ft)rm. as has been very fully shown 

 recently, for Colobocentrotus antl Podophora (\. Aga.ssiz, 1908, Mem. M. C. Z., 



xxxix. ri>. ;u and;vj). 



The calcnreous spicules of the pe<lirels. show an unusual diversity. They are 



