IvCIIIXOIDHA. II. 



29 



based on tlie true J-'.cli. pnsiUns — as is shown below — llie\- do not give a correct representation of 

 this feature in pnsiUiis. These pores are not most numerous above the ambitus, as is stated in tlie 

 diagnosis of the genus Echinocyaiiiits given in Re\ision of Echini ip. 304); on the contrar\', wliile 

 tliey occur in a single series along each suture alxive the ambitus the}' Ijccome (|uite crowded on tlie 

 actinal side, covering a considerable part of the plates and increasing in number towards the peristome 

 (PI. XII. Fig. 27). On the analysis of the test given by Loven (Etudes. PI. XLIVl the distribution of 

 these small pores is very carefully shown. I must add only that these pores are also found within the 

 petals, on the inner side of the double pores, though of course less numerous and diminishing in numbers 

 towards the apical s\stem, only one pore being found on the inner side of the upper pairs of pores of the 

 petals. (PI. XII. Fig. 31.) Outside the petals also a few small pores occur on both sides, but only at some few 

 of the outer pairs of pores. — In young specimens these small pores are few in number and rather difficult 

 to see; in quite small specimens no small pores are found within the petals. — The inner edge of the 

 ambnlacral plates adjoining the peristome is abruptl\- bent inwards and here two considerablv larger 

 pores are found (PI. XII. Figs. 26, 27), corresponding to two tube-feet distinctly larger than the numerous 

 small tube-feet which cover most of the actinal side. These larger tube-feet are evidentl\' homologous 

 to the large buccal feet of the Regular PZcliini; otherwise they differ from tlie small tube-feet onl\- in 

 size, and, like these, the\" are not provided with spicules or calcareous ring. 



De ^leijere (op. cit. p. 107) remarks that there must be some variation in the relative size of 

 the genital and ocular pores in pi/si/lii.s, referring to the figures given under that name b\- Agassi z 

 in .<Rev. of Echini. Having examined a large number of specimens of Ech. pitsilhis I find that the 

 genital pores are always larger than the ocular pores, (PI. XII. Fig. 31), and that the latter are generally 

 much smaller, though sometimes the difference is not very great. The difference in this respect between 

 the figure 3. PI. XL e. and figs, i and 6. PI. XIII in Rev. of Ecli. is due to the fact that these figures repre- 

 sent two different species, only the former being the true Ecli. piisiUiis. The genital pores appear \-ery 

 earl\-, in specimens of onh' c. 3'"'" length; I lia\e even seen specimens of only 2""" in which the geni- 

 tal openings were alreadv distinct. — As stated by Lo\-en (Etudes. PI. XVI. 139) there is onh' one 

 madreporic pore, situated near the anterior end of the apical s\stem. This feature is of some impor- 

 tance, giving a good distinguishing character between Ecliiiiocyainus and young specimens of Clypeasffr. 

 the number of madreporic pores beginning to increase early in the latter. (In a young Clypcastcr sp. 

 from vSt. Cruz of onl\- 5""" length I find 6 pores in the madreporic plate). 



The internal supports of the test as well as the depressions seen along the sutures between the 

 actinal ambnlacral plates are rather well shown on the figures PI. I. 12 — 13 of Forbes (Monogr. Ech. Brit. 

 Tert), and PI. XX\TI. 6- 7 of E. Agassiz. Costa also (op. cit. Fig. 2. C. D.) gives (rather coarse) figures 

 of the interior of the test. The figure given in Rev. of Ech. (PI. XIII. 7), differs very considerably 

 from those above cited; it is evidently another species. A detailed description of these internal struc- 

 tures need not be given, I ma\' refer to the figures gi\en by F"orbes and L. Agassiz and to the 

 one given here (PL XII. Fig. 29) for comparison with the EcIi. grand/poms described below. It will be 

 remarked that the radiating supports continue as far as to the peristome; on the abactinal side the\ onl\- 

 continue to the outer end of the petals. These ridges are formed by the edges of the interambnlacra. 

 The ambxdacra .show, as seen from the inside, a fairly deep depression along each transverse suture, the 



