4 8 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
surrounded by numerous smaller plates. The character that the ocular plates are 
all excluded from the anal area is, unfortunately, not constant. Certainly it is 
generally the case, which then gives a good distinguishing character, but in some of 
the specimens in hand, which I am otherwise unable to distinguish from the typical 
form, one or even two ocular plates are in contact with the anal area, viz. in two 
specimens Ocular I, in one specimen (Stat. 20) Oculars I and V. The latter speci- 
men, however, is probably a hybrid between St. Agassizii and Neumayeri. (The 
shape of its test is as in Agassizii, but the secondary tubercles on the actinal side 
are less prominent than is generally the case in Agassizii, and the central plate is 
quite indistinct as is the case in the larger specimens of Neumayeri. There are 
numerous spicules as in Agassizii; the globiferous pedicellariæ are of the form 
typical in Agassizii. — It may be noticed that St. Neumayeri is represented from 
the same station.) Of the two other specimens one is that mentioned above, in 
which the scrobicular areas are separated throughout the whole series (Stat. 16), the 
other is a small specimen, 29 mm. (Stat. 22). As there is evidently no reason for 
regarding these specimens as hybrids, it must be conceded that the character of all 
the ocular plates being excluded from the anal area is not quite constant; in most 
cases it is found, however. — Generally there are distinct genital papillae, as in the 
other Sterechinus- species. The genital openings are present already in the youngest 
specimen, 1 1 mm. diameter. (A still younger specimen, 7 mm., has likewise the 
genital openings developed; the identification of this specimen is, however, not 
certain.) 
The peristome is rather small, generally smaller than in diadema. The buccal 
plates usually carry one or two small spines. 
The spines are like those of diadema; they are very fragile as in all the Ster- 
echimis- species. The secondary spines are upon the whole slightly longer than those 
of diadema; they are slender and finely thorny as in that species, ending in a small 
central thorn or gradually tapering to a point; the latter case seems always to occur, 
where the point has been restored, which is very often the case (PI. XVI. Figs. 
7, 13). (The mark, from where the restored part begins, is very distinctly seen by 
microscopical examination.) 
The globiferous pedicellariæ have generally the blade almost quite open, as 
stated by DöDERLEIN; but sometimes there are crossbeams over the lower half of 
the blade, or even almost to the end of it — and both kinds may be found in the 
same specimen. The poison-glands are single, but with double efferent duct (PI. XVI 
Fig. 15), as is also the case in the other Sterechinus- species, in marked contrast to 
Notechimis, where the glands are double. DÖDERLEIN describes the tridentate pedi- 
cellariæ as having almost parallel side-edges; this is, however, generally the case 
only in small specimens, whereas in larger ones the shape of the valves is that 
