ECHINOIDEA. I. 113 



(PI. XXI. Fig. 3) is found, with a broader blade and less developed mesh-work; the part where the 

 val ves joiii, is comparatively larger than in the large form; transitional forms are found. The ophice- 

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

 the common form. The spicules of the pedicellariæ 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 membraiie numerous small spicules are found 

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



Tripnc2isics drprcsstis A. Ag. is, with regard to spicules and pedicellariæ, quite similar to cscii- 

 lf-iifits\ I have not, however, been able to find tridentate and trijihyllous pedicellariæ on the only, 

 badly preserved specimen before me. As in fsailcnfus only ever>- third or fourth ambulacral plate has 

 a primary tubercle. The difference between the two species is \-ery well given in Rev. of Ech. 



Tripnciisfcs v(in',-gaf/(s (Leske). A primary tubercle is only found on every third ambulacral 

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

 distinguished with difficulty, while in i'sciih'//h(s the primary tubercles form a beautiful, rather con- 

 spicuous series. As in csailciifus two ocular piates reach to the i^eriproct; no central plate. The buccal 

 membrane with numerous thick fenestrated piates carr\-ing pedicellariæ; even globiferous pedicellariæ 

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

 pedicellariæ quite as in csc/i/ciifus, the tridentate ones resemble very much the smaller form in cscu- 

 Icu/hs\ a form corresponding to the larger form in this species I have not found in T. varifgafus. 

 Ophicephalous and triphyllous pedicellariæ as in fsailciifiis; the spicules of the pedicellariæ typically 

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

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

 dumb-bell-shaped ones. According to Loven (252) this species corre.sponds to Linné's Echimis Gra- 

 Hlla\ this name must then be adopted instead of varicgatus (Leske). 



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

 and Tripu-ciistcs [Hipponor] are chiefly distinguished by the faet that in Toxopneiistcs the pores are 

 arranged in oblique arcs of three pairs, while in Tripneusfcs 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- 

 pneustcs the pores may form three irregular longitudinal series as in Tripneiistes^ what has already 

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

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

 as in Toxopneustcs without an>- 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 

 esculcnfiis^ dcprcssiis, and grafilla form a group that is, as to their habitus, very different from the 

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

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

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



The In?olf-Expedition. IV. i. 1 5 



