532 ECHINODERMATA ECHINOIDEA 



usually differ very much in species of the same genus. In the 

 vast majority of species there is a limited number of long spines 

 called " primaries," amongst the bases of which a large number 

 of much shorter " secondaries " are distributed. In ' Cidaridae 

 the primaries are very long and thick and blunt at the ends, and 

 the secondaries form small circles around their bases. The 

 primaries in Cidaridae and the tips of the primaries in 

 Arbaciidae and Echinothuriidae are covered with a special 

 investment of extremely close, hard, calcareous matter very 

 different from the loosely fenestrated material out of which 

 the bodies of the spines of all species are composed. In 

 Colobocentrotus and Heterocentrotus the primaries are very thick 

 and triangular in section, whilst the secondaries on the aboral 

 surface have expanded outer ends, which form a close-set pave- 

 ment protecting the ectoderm from the shocks of the breakers. 

 In Echinothuriidae the primaries are short and so delicate as to 

 be termed silky. 



Pedicellariae. In Cidaridae only gemmiform and tridactyle 

 pedicellariae are found. In the gemmiform the glands lie 

 inside the grooved blades instead of outside as normally, and 

 they are covered internally by ingrowths of calcareous matter 

 from the edges. In Echinothuriidae only tridactyle and trifoliate 

 are found in most species, but rudimentary gemmiform are found 

 in one species and well-developed ophicephalous in another. In 

 some species (Centrostephanus longispinosus) there are found 

 gemmiform pedicellariae which have lost the jaws but retained 

 the glands. These are termed " globiferae." Mortensen 1 uses 

 minute details in the structure of the pedicellariae to discriminate 

 species and even genera, but in this the present author is not 

 prepared to follow him. 



Tube-feet. The tube-feet belonging to the aboral surface are 

 pointed and devoid of a sucker in Diadematidae, Echinothuriidae, 

 Arbaciidae, and Cidaridae; 2 in the last-named family those 

 belonging to the oral surface have suckers, in the centre of 

 which a pointed (sensory) prominence is to be noted. 



The classification of the Endocyclica is by no means in a 

 satisfactory condition, and different authorities have arrived at 



1 Dcmish Ingolf Expedition, " Echinoidea," pt. i. 1903. 



2 Prouho, " Recherches sur le Dorocidaris papillata et quelques autres Echinides 

 de la Mediterranee," Arch. Zool. Exp. (2) v. 1887, p. 308. 



