ECHINOIDEA. II. .g 



and PI. XL\'. Figs. 30— 31 i.s evidently this form of tridentate pedicellariæ. (The figure 31. PI. XLV 

 is, otherwise, not the tip of the blade as stated in tlie explanation of piates — though the expression 

 «blade is, of course, not used — , bnt a fragment of the articular surface seen from above). The ophiceph- 

 alous pedicellariæ (PI. IX. Fig. 13) have rather elongate valves; the fine teeth along the outer edge 

 of the blade do not continue along the edges down the apophysis, as is the case in Urech. naresianus 

 and the other species related thereto; only a few coarse serrations are found along the sides of the 

 apophysis. The basal part is distinctl\- developed, though not reaching the outer widened part of the 

 valve. The arc is distincth- developed on all the valves; the upper end of the stalk is cupshaped. The 

 triphyllous pedicellariæ (PI. IX. Fig. 29) are somewhat different from those of the other species of 

 &Cystechimisy>; the valves are more elongate and spoon-shaped and more narrowed below than is the 

 case in the other species. 



The description of Cystccli. clypeahcs given in the Challenger»-Echini is evidently made after 

 this species. I can only add that the piates are large and very thin, with concentric lines (marks of 

 growth), and that the abactinal pores are simple. The ver\- thick miliary spines, represented in PI. 

 XLV. Fig. 29 of the Challenger -FIchini are found on the anal area of this species. The primary spines 

 are brownish at the base, white ni the outer part; they are (some of them at least) coarsely serrate 

 in the outer part. 



That the thickplated and the thinplated form represent two very distiuct species is beyond 

 doubt; auother question is, which of them must keep the name clypeatiis, and that is not so easily 

 solved. It is certain that the figures given in the Challenger -Echini represent the thinplated form, 

 and the description likewise is evidently made from this. But on the labels of the thinplated speci- 

 mens (St. 133 and 334) there is a mark of interrogation (though this doubt is, as usual, not mentioned 

 in the text], which seems to indicate that Professor Agassiz himself regarded the thickplated form 

 as the t>pe of the species, as seems also to be indicated by the name clypeatiis. However, considering 

 the faet that the species described and figured under that name is really the thinplated form, I think 

 it correct to let this species keep the name Cysfecliiiins chpeafiis. The thickplated form (St. 205) must 

 then have auother name; but since its structure is almost quite uuknown, so that, in faet, \ve cannot say 

 to which genus it belongs (probabl\ a new genus), I thnik it better to let it remain uiniamed for the present. 



<' Cystccliiiius • (Urccliinus) ]]'yvillii. Four kinds of pedicellariæ have been found, viz. globi- 

 ferous, tridentate, ophicephalous and triphyllous. The globiferous pedicellariæ (PI. IX. Figs. 3, 5, 24) are 

 essentialh- like those of Ureelt, gigantens, only the blade is shorter and more curved; there is gener- 

 ally only one tooth on either side of the terminal opening, sometiraes, however, there are two on either 

 side. The tridentate pedicellariæ occur in two forms : a more slender form, ver\- similar to that of 

 U. naresianus. and a larger more coarse form (PI. IX. Fig. 17), generally more or less irregular in the 

 lower part of the blade; size up to ca. o-8""". These two kinds are, however, not sharply distinguished, 

 all transitional forms being found. The figures given in the Challenger -Echinoidea PI. XLII. 13 and 

 XLV. 28 as large-headed (Spatangoid-like) pedicellariæ evidenth- represent the larger form, though 

 a less coarse specimen than that figured here. The ophicephalous pedicellariæ are ^'ery like those of 

 U. gigantetis; the head of an ophicephalous pedicellaria is represented, though not \er\- clearly, in the 

 figure 27. PI. XLV of the Challenger -Pvchini, under the name of a Clypeastroid-like» pedicellaria. 



The Injolf-Kxpedition. IV. 2. n 



