TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
plates are widely excluded from the anal area, exceptions may occur; of three spe- 
cimens from Ultima Esperanza (Fuegian Expedition 1896) two have two of the ocular 
plates in broad contact with the anal area, and the third specimen has one ocular 
plate almost in contact with the anal area. These specimens do not otherwise differ 
from the typical ones. — The anal plates are always arranged in the same manner, 
the short diagonal going from about the middle of the madreporite to the ocular V. 
This position of the anal plates appears to be the rule in the Arbaciidce , except, of 
course, those with 5 anal plates ( Pygmæocidaris , Habrocidaris). 
TROSCHEL, in his description of A. Dufresnii (Op. cit. p. 321), mentions »haar- 
förmige Stachelchen» which are carried by the small granules between the tubercles. 
Also De Loriol (Op. cit. p. 11) says that »les radioles des granules ont l’apparence 
de soies assez longues, d’une délicatesse extrême». It is quite beyond doubt that 
these »spines» are only the pedicellariæ (or the stalks of pedicellariæ which have lost 
the head).* Small thin spines upon the whole do not occur in the Arbaciidce ; also 
the short secondary spines are thick and coarse. 
The pedicellariæ I find, upon the whole, as described and figured by AGASSIZ 
& CLARK. They are, however, somewhat variable. In one of the specimens from 
the Fuegian Expedition ( 23 /i 96) the tridentate pedicellariæ have a peculiar form 
(PI. XV I'ig. 13), being somewhat abruptly widened above the basal part; but in 
other specimens from the same locality they have the typical form shown by the 
fig. 5 PI. 47 in Agassiz & Clark’s work. The ophicephalous pedicellariæ generally 
are of the form figured by Agassiz & Clark (PI. 47. Fig. 7) but another form 
(PL XV Fig. 6) also occurs, though much less numerously, in which the blade is 
only about half the length of the basal part. The upper end of the stalk of the 
ophicephalous pedicellariæ I find somewhat different from the figure given by 
Agassiz & Clark (PI. XV Fig. 10 to compare with PI. 47. Fig. 4 in the work of 
AGASSIZ & Clark). Also the triphyllous pedicellariæ I find a little different from 
the figure given by Agassiz & Clark (Fig. XV Fig. 2 to compare with PI. 47. 
Fig. 6 in AGASSIZ & Clark’s work). This figure shows a broad coverplate passing 
upwards along the sides of the blade; I have seen nothing like that in my prepara- 
tions. In the text the authors say (p. 69) that there is no »coverplate», in contra- 
diction to the figure. Otherwise I may only remark that the triphyllous pedicellariæ 
are finely serrate along the edge of the valves. 
Agassiz & Clark state that »calcareous particles appear to be quite wanting in 
the walls of the pedicels, except for the terminal rosettes and their supporting rods 
in those of the actinal surface». I have, however, in some cases found some few 
* Ch. Desmoulins (Sur les épines des Échinodavites. Act. Soc. Linn. Bordeaux T. XXVII. 1S69. p. 5) 
also describes such t épines pilif ormes .... qu’on oserait à peine nommer miliaires* , which are evidently 
likewise the stalks of pedicellariæ. 
