ECHINOIDEA. I, 



163 



With regard to the other .synoiunis and the iiimieiise number of places in the literature where 

 this species is mentioned or more thoroughly treated, the reader is referred to Rev. of Ech. and 

 Bell's Catalogue. — As it has been treated so man\- times, I shall only here mention a few features 

 that have not before been described with sufficient clearness. 



With regard to the provision of the test with tubercles very great variation is found. On 

 PI. XVI. Fig.s. 17 and 23 is represented an ambulacral and an interanibulacral area of a specimen 

 with comparativeh- few tubercles (Sars's Sfr. pallidas). Figs. 11 and 21 represent the same of a 

 specimen with numerous tubercles [granularis Say). The difference is here very conspicuous, and 

 nevertheless the represented forms are by no means extreme ones. All transitional forms between 

 these may be found. The nirmber of the pores varies between 4 — 7, but most commonly 5 or 6 are 

 found. Generally two ocular plates reach to the periproct (PI. XVI. P'ig. g), sometimes three, more 

 rareh" one. On PI. XVI. Fig. 4 is figured the apical area of a specimen with two pores in one of the 

 genital plates. 



The buccal membrane contains rather numerous fenestrated plates some of which are large, 

 very complicated, and carry pedicellarise; those inside of the buccal plates are, as usual, smaller 

 (PI. XVI. Fig. 13). Very few bihamate spicules in the buccal membrane and the gills, which latter 

 otherwise contain the usual irregular fenestrated plates. 



The pedicellarise. It was the pedicellarise of this species which were figured by O. F. Miillcr 

 in Zoologia danica; among the later authors only Perrier') has studied them more thoroughh' and 

 figured some of the skeletal parts. Also Agassiz gives some figures (Rev. of Ech. PI. X), but the\- 

 are too small to show the interesting features found here. — The globiferous pedicellarise (PL XX. 

 Figs. 16, 25, 26, and 29) are highly characteristic and widely different from those of all the other Eclii- 

 nids occurring in the northern Atlantic. The head is not, as in those, placed directh- on the stalk, 

 but connected with it by a long, muscular neck, provided with as well longitudinal as circular muscles, 

 so that it may be stretched out and retracted, and the head ma\' be moved freely in all directions. 

 The blade is tubular, without lateral teeth, only with a more or less marked obliquity above. Per- 

 rier's figure (PI. V. Fig. 7. a) of such a valve is rather unfortunate, as it seems to show two end-teeth. 

 The form of the basal part is rather varying, as the outer corners may be more or less conspicuous 

 or bent somewhat inward. Most frequently some spicules are found in the head, arranged in a narrow 

 band along the edge of the valves (Fig. 29). The stalk is a hollow tube peculiarly furrowed above. 

 (Also the stalks of the other pedicellariae are hollow.) The globiferous pedicellarise are generall\- 

 large and strong; they are sometimes found in so great numbers as to be almost more conspicuous 

 than the spines (on the abactinal side). Sometimes they are quite light, sometimes quite dark from 

 pigment; the more pigmented they are, the fewer spicules they seem to contain; the\- may also quite 

 want spicules. 



The tridentate pedicellariae are of very different forms (PI. XX. Figs. 4, 6, 20); the blade may be 

 long and narrow, or short and broad, deep with almost adjoining edges, or flat and broad; now there 

 is a strong mesh-work, now almost none. The ophicephalous and triphyllous pedicellarise (PI. XX. 

 Figs. 3, 5) without marked peculiarities. — The spicules (PI. XX. Fig. 12) are branched at the ends, but 



■) Recherches sur les Pedicellaires. p. 152. 



21* 



