ECHINOIDEA. I. 



i i 



Tripneustes they are dump-bell-shaped, and in many genera they are irregular, perforated calcareous 

 plates. Perrier (op. cit.) and especially Stewart') have figured the spicules of many Echinoids; but 

 they have not, any more than the pedicellarise, hitherto been of any importance in the classification. 

 The sphaeridia do not appear to show such differences in structure that they may yield system- 

 atic characters. On the other hand the structure of the spines is of no small systematic importance, 

 as especially shown by Mackintosh (264 — 265), and they are never to be passed by in the descrip- 



- $& V- 



! 



■hi. 



Fist. I. 



Fig. 2. 



Fig- 3- 



Fig. 4. 



Fig. 1. Valve of a globiferous perlicellaria of Parechinus miliaris (Mull.) 



— 2. — - an ophicephalous pedicellaria of Strongylocentrotus drebachiensis (O. F. Mull.) 



— 3. — - a triphyllous pedicellaria of Parechinus miliaris. 



— 4. — - a tridentate pedicellaria of Strongyloc. drebachiensis. 



In all the figures a. means the apophysis, A. the basal part, bl. the blade, e.t. the end-tooth, s.t. lateral teeth, /. the articular surface. 



tions — as indeed nothing that may be of systematic importance. Above all, the most easily acces- 

 sible and most reliable characters, viz. the pedicellarise and spicules, ought never to be omitted in 

 systematic descriptions of Echinoids. 



Fam. Cidaridae. 



With regard to the classification of the Cidarids, all authors seem to agree in only one thing, 

 viz. that all attempts made hitherto at giving a natural limitation to the genera have failed. Every 



■I On the Spicula of the Regular Echinoidea. Transact. Linn. Soc. London. XXV. 1865. p. 365—71. PI. 47 — 50. 



