064 PEDICELLARIAE. 



of the base and of the spathiform prolongation; the latter is in Echinothrix 

 wider than the base, the opposite is the case in Echinidae proper. The 

 limestone rod of the shaft is slender, with a large terminal head ; the soft 

 parts surrounding the head and shaft are greatly developed. I have figured 

 the small broad-headed pedicellariae of Asthenosoma in the Hasslcr Echini. 

 The buccal pedicellariae of the Diadematidae differ from those of the Echi- 

 nidae in having a solid base (PL XXIV. f. 3?'). 



The pedicellariae of the Arbaciadae are of two kinds. Those near the 

 actinostome have a short muscular shaft seated upon a long base, strength- 

 ened internally by a slender rod ending in a broad head. The muscular 

 base supports a stout head (PL XXVI. f. 4,5), with strong sharp teeth near 

 the tip. The other kind differs only in the length of the upper muscular 

 sheath and the solid, nearly bare calcareous shaft supporting it, In the 

 abactinal part of the test the long-stemmed pedicellar'ue (PL XXVI. f. 3) 

 arc especially abundant in the interambulacral spaces close to the anibu- 

 lacral areas. The muscular sheath is so long that in alcoholic specimens the 

 weight of the head is sufficient to bend it over; when living, these pedi- 

 cellariae are most active, reaching out in all possible directions. In Podoci- 

 daris the pedicellariae occur over the whole abactinal surface (PL IV. f. s), 

 the head is still larger in proportion to the length of the shaft, than in Arbacia, 

 and. as has been mentioned already, they are supported upon small tubercles 

 with distinct scrobicular circles. 



In the Echinometradae, as limited here, the pedicellariae do not differ very 

 essentially from those of the Echinidae proper, and we can apply to them the 

 terms introduced by Valentin to denote, according to their position and 

 shape, the different kinds of pedicellariae. The buccal or ophicephalous 

 pedicellariae are short-stemmed, stout-headed, the base ending in more or 

 less complicated and regular semicircular arcs (PL XXVI. f. s). They arc 

 figured with their soft parts in S. Drbbachiensis, in PL X. f. 0,10, and the 

 calcareous prongs in PL XXIV. f. 17,19,21; other ophicephalous pedicel- 

 lariae of Strongylocentrotus are figured in PL XXIV. f. ..>:, and of Stomo- 

 pneustes in PL XXIV f. 32. The gemmiform pedicellariae are remarkable 

 for the great development of the soft parts, and the slender prongs of the 

 heads, usually terminating in two large hooks, placed one above the other in 

 Echinometradae (PL XXIV f. 18,24; PL XXVI f. 10.14), while they are 

 nearly on the same level in Echinidae proper. The third kind are the long- 

 headed tridactyle pedicellariaa, in which the calcareous parts take the greatest 



