28 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 {Pygmœocidaris, Habrocidaris). 



Troschel, in his description of A. Diifresnii (Op. cit. p. 321), mentions »haar- 

 formige Stachelchen ^ which are carried by the small granules between the tubercles. 

 Also De Loriol (Op. cit. p. 11) says that xles 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 pedicellariœ (or the stalks of pedicellariae which have lost 

 the head).* Small thin spines upon the whole do not occur in the Arbaciidœ: also 

 the short secondary spines are thick and coarse. 



The pedicellarire I find, upon the whole, as described and figured by Ag.\,S.SIZ 

 & Clark. The}- are, however, somewhat variable. In one of the specimens from 

 the Fuegian Expedition ('V' 96) the tridentate pedicellariae have a peculiar form 

 (PI. XV Fig. 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 PL 47 in Ag.ASSIZ & Cl.VRK's work. The ophicephalous pedicellariae generally 

 are of the form figured by AgasSIZ & Clark (PI. 47. Fig. 7) but another form 

 (PI. 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 pedicellariae I find somewhat different from the figure given by 

 Agassiz & Clark (PI. XV Fig. 10 to compare with PL 47. Fig. 4 in the work of 

 Agassiz & Clark). Also the triphyllous pedicellariee I find a little different from 

 the figure given by AGASSIZ & Clark (Fig. XV Fig. 2 to compare with PL 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 xwy 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 pedicellariae 

 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 Échinodarites. .4ct. Soc. Linn. Bordeaux T. XXVII. 1S69. p. 5) 

 also describes such >cfines filiformes .... qu'on oserait .i peine nommer miliaire^y, which are evidently 

 likewise the stalks of pedicellariae. 



