PEDICELLARLE. 665 



development (PL X. f. 7,11,12); the prongs have a triangular base and a 

 more or less spoon-shaped tip, slightly serrated, as in Strongylocentrotus 

 Drobachiensis (PL XXIV. f. 15,16,22,23), S. lividus (PI. XXIV. f. 25), 

 S. nudus (PI. XXIV. f. 26, 28), Stomopneustes variolaris, (PI XXIV f. si), 

 and in Echinometra (PI. XXVI. f. 9, 11, 12, is). In Heterocentrotus (PI. 

 XXVI f. 1,2) the tridactyle pedicellariae are of the type called trifoliate; 

 in Echinometra (PI. XXVI. f. n) there is no doubt these trifoliate pedicel- 

 lariae are only the younger stages of the tridactyle forms. 



The principal differences between the pedicellaria? of the Echinidae proper 

 and the Echinometraclae consist in the position of the hooks of the gemmi- 

 form pedicellariae, which invariably terminate on one level, both in the 

 Triplechinidae (PL XXV. f. 4, 16, 17,20) and in the Temnopleuridae (PL 

 XXV f. ,.'). The differences in the ophicephalous pedicellariae of the two 

 families are not very marked; compare (PI. XXV. f. l, 14, 19, 2l) the pedi- 

 cellariae of Temnopleurus, of Echinus, and of Toxopneustes with those of 

 Echinometra and of Strongylocentrotus referred to above. The same is the 

 case with the tridactyle pedicellariae of the Temnopleuridae (PL XXV f. 1, 2) 

 and of the Triplechinidae (PI XXV. f. 3, 5, 6, 11, is); they agree most closely 

 with the corresponding pedicellariae of the Echinometradae, — the principal 

 distinction consists in the more slender, spoon-shaped prong. 



In the Clypeastridae we find great differences in the pedicellaria? ; in some 

 cases they approximate closely to the tridactyle pedicellariae of the Echinidae 

 and Echinometradae, — see one of the prongs of a tridactyle pedicellaria of 

 Clypeaster subdepressus (PL XXV f. 24, 25', 42), or the more elongate type of 

 the same species (PL XXV. f. 22), — while what must be considered the 

 ophicephalous pedicellaria? of Echinanthus take most extraordinary shapes 

 (PL Xl f . f. 6-9)- Another form of pedicellaria? is the hemispherical kind, 

 supported upon a long, slender, flexible, muscular shaft attached to a base, 

 strengthened by a comparatively stout rod ( PL XI f . f. 10, 11 ). 



In Echinarachnius the pedicellaria? have but two prongs, as in the hemi- 

 spherical pedicellaria? of Echinanthus. They are supported upon a short, 

 stout, calcareous rod, at the base of a long, powerful, muscular band, support- 

 ing a comparatively small bifid head. PL XXVI. f. 15, 16 ; PL XXV. f. 38, 39, 

 represent them in different attitudes. PL XXVI. f. it, is ; PL XXV. f. 40, 41, 

 are various stages of growth, although I have not had occasion to examine 

 the pedicellaria? of a large number of Clypeastroids, yet the great variety of 

 the forms observed is very remarkable. 



