ECHINOIDEA. I. 



II 



Tripneustcs tlie}- are dump-bell-shaped , and in many genera they are irregular, perforated calcareous 

 piates. Perrier (op. cit.) and especially Stewart') have figured the spiciiles of many Ecliinoids; but 

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

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

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

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



Fig. r. 



Fij;. 2. 



Fig. 



Fig. 4. 



Fig. I. Valve of a globiferous pedicellaria of Parechimts milians (Miill.) 



— 2. — - an ophicephalous pedicellaria of Strongylocentrotus drobachiensis (O. F. Miill.) 



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



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



In all the figures a. means the apophj-sis, b. the basal part, bl. the blade, e.t. the end-tooth, s.t. lateral teeth, /. the articiilar snrface. 



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

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

 systematic descriptions of Echinoids. 



Fam. Cidaridæ. 



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. l'l. 47—50. 



2* 



