ECHINOIDEA. I. 113 



(PI. XXI. Fi<^-. 3) is found, with a broader blade and less developed niesh-work; the part where the 

 valves join, is comparatively larger than in the large form; transitional forms are found. The ophice- 

 phalous pedicellarise shorter and broader than usual (PI. XXI. Fig. 22); the triphyllous pedicellarise of 

 the common form. The spicules of the pedicellarise are typically dumb-bell-shaped (PI. XXI. Fig. 33. a); 

 in the tube feet common bihamate spicules are found together with very small spicules, also bihamate 

 (Fig. 33. b) or a little dumb-bell-shaped; in the buccal membrane numerous small spicules are found 

 with truncate ends (Fig. 33. c) together with larger bihamate spicules (Fig. 33. d). 



Trip)inisfcs dcpressus A. x\g. is, with regard to spicules and pedicellariee, quite similar to rsai- 

 lriitiis\ I have not, however, been able to find tridentate and triphyllous pedicellaria; on the only, 

 badly preserved specimen before me. As in csculcntus only every third or fourth ambulacral plate has 

 a primar}- tubercle. The difference between the two species is very well given in Rev. of FCch. 



Ti-ipiicustcs tiaricgatns (Leske). A primary tubercle is only found on every third ambulacral 

 plate; the secondary tubercles almost as large as the primary ones, so that the latter are only to be 

 distinguished with difficulty, while in csciilriitus the primary tubercles form a beautiful, rather con- 

 spicuous series. As in esculent us two ocidar plates reach to the periproct; no central plate. The buccal 

 membrane with numerous thick fenestrated plates carrying pedicellarise; even globiferous pedicellarise 

 may be found on the buccal membrane, a fact I have not seen in any other Echinid. The globiferous 

 pedicellarise quite as in esculeufus, the tridentate ones resemble very much the smaller form in escti- 

 lcnfus\ a form corresponding to the larger form in this species I have not found in T. variegatus. 

 Ophicephalous and triphjdlous pedicellarise as in csculcntus; the spicules of the pedicellarise typically 

 dumb-bell-shaped; in the tube feet only really dumb-bell-shaped spicules seem to be found, in the buccal 

 membrane there are comparatively few spicules, partly larger, bihamate ones, partly smaller, somewhat 

 dumb-bell-shaped ones. According to Loven (252) this species corresponds to Linne's Echinus Gra- 

 tilla\ this name must then be adopted instead of variegatus (Leske). 



According to the definition given by Agassiz (Rev. of Ech. p. 297 seq.) the genera Toxopneustes 

 and Tripncustcs {Hipponoe) are chiefl\- distinguished by the fact that in Toxopfieustes the pores are 

 arranged in oblique arcs of three pairs, while in Tripncustcs the pores form three vertical series; the 

 series in the middle is irregular, the two outer ones are regular. The other characters — whether the 

 peristome is large or small, and whether the tubercles form more or less regular vertical and hori- 

 zontal series — are of a so relative nature, that it will be better to leave them out of consideration. 

 Unfortunately the mentioned principal character is not reliable either; in larger specimens of Toxo- 

 pneustes the pores may form three irregular longitudinal series as in Tripneustes^ what has already 

 been mentioned by Agassiz in his diagnosis of the genus Toxopneustes, and in smaller specimens of 

 Tripncustcs^ up to a diameter of ca. 20™'", the pores are arranged in quite similar arcs of three pairs 

 as in Toxopjicustcs without au}- indication of an arrangement in longitudinal series. Accordingly none 

 of the characters hitherto pointed out are reliable. It must, however, be admitted that the species 

 csculcntus, dcpressus, and gratilla form a group that is, as to their habitus, very different from the 

 species referred to Toxopneustes, so that it seems natural to keep them as a separate genus. To this 

 is to be added that, if the genera Toxopnettstes and Tripncustcs were to be united, it would give rise 

 to a complete rearrangement of the nomenclature; especially the name of Toxopneustes would then have 



The In^olf-Expedition. IV. i. 15 



