10 BULLETIN 74, UNITED STATES NATIONAL MUSEUM. 



variation nino;ino; from the typiciil fuini to that with a large terminal opening and 

 without an end tootii, resembhng those of StyJocidaris ajfinis. Concerning this 

 extraordinary variation I may first point out tliat the figure 6 in my opinion represents 

 a young, not yet fully developed pedieellaria" and that figure 9 has very much the 

 appearance of having the end tooth broken. But the figures 7 and 8 can not thus be 

 ilisjjosed of; Doctor Clark has informed me that he is absoutely certain that they 

 reall}- belonged to the same specimen, and it is also said in the explanation of the 

 plate that the form represented by figure 7 was quite common. The specimen in 

 wliich these dilTerent forms of pedicellaria; were found is that figured by Clai-k in 

 The Cidaridae Plates 8-9, as Doctor Clark has informed me, namely, a specimen 

 with the radioles of the unusual smooth form, so ilifferent from the typical spinous 

 form. Agassiz and ('lark do not indicate that they have found the difi'erent forms 

 of pedicellariiu in any other specimen, and I, for my part, have found only the 

 form with the small pore in all the specimens examined with spinous radioles; in the 

 specimen with smooth radioles I have found a single globiferous pedicellaria of the 

 Stylocularis form among very numerous pedicellariae of the typical form. On 

 account of the uncommon form of the radioles in the specimen figured by Clark and 

 the fact that two diii'erent forms of large globiferous pcdicellariae occur in this speci- 

 men I ventured to suggest, in my work Die Echinoiden der deutschen Siidpolar 

 Expedition (p. 47), that it is a hj^brid between Tr. hartletti and Styloddans ajfinis. 

 Having now had occasion to examine such a specimen myself, I feel strengthened 

 in this opinion. On comparing this specimen with the typical form, one would 

 at first refuse to regard the two as belonging to the same species, so different are 

 they in appearance. But a close examination does not reveal any other features 

 than the radioles by which to distinguish them, except the peculiar occurrence of 

 the two forms of gloI)iferous ])edicellarise. I do not, of course, maintain upon 

 such scanty material that it is proved that the form with the smooth radioles is 

 really a hybrid, but it seems to me a natural explanation of this peculiarity. 



STYLOCIDARIS '' LINEATA, new species. 

 Plates 4-6; plate 7, ti^s. 3-.5; plate 14, fig. 10; plate IG, fig.s. (1, 9; plate 17, figs. 4, S. 



The shape of the test is very like that of Stylocidaris ajfinis, so that in this feature 

 or in the relative proportions of the parts of the test scarcely any tlilTerence between 

 the two species can he found. The ambulacra alone aifonl a difference, which 

 appears to be constant and thus of value as a specific character. In all the four 

 specimens at hanil each ambulacral plate carries only one small tubercle within and 

 a little below the primary tubercle; there is thus a rather broad bare median space 

 left between the two ijuite regular series of tubercles (Plate 14, fig. 10). In St. 

 ajfinis this also holds good in the younger specimens, but in the larger ones each 

 ambulacral plate (at the ambitus) carries another smaller tubercle at the upper edo-e 

 of the plate, the inner series thus becoming irregular and the median naked space 

 less conspicuous (Plate 14, fig. 1). This third tubercle makes its appearance at a 



Agassiz and Clark (Hawaiian Echini, p. 8) have mentioned this as being po.ssible but not probable. 

 b Concerning the name Slytoeidaris, reference should be made to my work Die Echinoiden der 

 deutschen Siidpolar Expcdilioii, ji. o2. 



