. The Cambridge natural history. Zoology. 534 ECHINODERMATA ECHINOIDEA The auriculae are incomplete and consist only of pillars arising from the interambulacral plates. The ambulacral pore- plates remain disunited, and the pores are arranged in a single vertical series; hence the ambulacra are very narrow. The inter- ambulacral plates each bear one large primary spine surrounded by several circles of secondaries. No ophicephalous or trifoliate pedicellariae are to be found, and the gland of the gemmiform pedicellaria is placed inside the concavity of the blade. The Cidaridae are in many respec
. The Cambridge natural history. Zoology. 534 ECHINODERMATA ECHINOIDEA The auriculae are incomplete and consist only of pillars arising from the interambulacral plates. The ambulacral pore- plates remain disunited, and the pores are arranged in a single vertical series; hence the ambulacra are very narrow. The inter- ambulacral plates each bear one large primary spine surrounded by several circles of secondaries. No ophicephalous or trifoliate pedicellariae are to be found, and the gland of the gemmiform pedicellaria is placed inside the concavity of the blade. The Cidaridae are in many respects the most primitive of the six families living. They are distributed all over the world, and chiefly inhabit deep water. No two naturalists agree as to how they are to be divided into genera. Mortensen,'' who takes the. anus periproct. anus Fig. 236.—Figure sliowingperiprocts of A, Cic^aris ; B, ^cAmmm. x 1. amS, Ambulacral plate ; , genital opening ; g,p, genital plate ; inter, interambulacral plate ; , madreporite ; oc, ocular pore. structure of the pedicellariae as his principal guide, recognises fourteen genera. Others (as for instance Bell) have been inclined to attribute nearly all the living species to one polymorphic genus, Cidaris, finding all attempts to divide the genera from one another frustrated by the discovery of transitional forms. Ooniocidaris (Fig. 237), however, dis- tinguished by its comparatively broad poriferous zones, by bare places in the middle line of both radii and interradii, and by deep pits on the lines of suture of the plates, is by general consent distinct. This genus is confined to the Eastern Pacific, but from British waters three species of Cidaris have been recorded, only one of which, C. (Dorocidaris) papillata, is at all common. It is found in water from 100 to 500 fathoms in depth ^ Loc. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration a
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