ECHINOIDEA. II. 



2 9 



based on the true Ech. -pusillns --as is shown below they do not give a correct representation of 

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

 diagnosis of the genus Echinocyamus given in Revision of Echini (p. 304); on the contrary, while 

 they occur in a single series along each suture above the ambitus they become quite crowded on the 

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

 (PL XII. Fig. 27). On the analysis of the test given by Loven (Etudes. PL XLIV) 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 system, only one pore being found on the inner side of the upper pairs of pores of the 

 petals. (PL 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 

 ambulacral plates adjoining the peristome is abruptly bent inwards and here two considerably larger 

 pores are found (PL 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 evidently homologous 

 to the large buccal feet of the Regular Echini; otherwise they differ from the small tube-feet only in 

 size, and, like these, they are not provided with spictiles or calcareous ring. 



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

 the genital and ocular pores in pusillus, referring to the figures given under that name by Agassiz 

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

 genital pores are always larger than the ocular pores, (PL 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. PL XL e. and figs, i and 6. PL XIII in Rev. of Ech. > is due to the fact that these figures repre- 

 sent two different species, only the former being the true Ech. pusillns. The genital pores appear very 

 early, in specimens of only c. 3 mm length; I have even seen specimens of only 2 mm in which the geni- 

 tal openings were already distinct. -- As stated by Loven (Etudes. PL XVI. 139) there is only one 

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

 tance, giving a good distinguishing character between Echinocyamus and young specimens of Clypeaster, 

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

 from St. Cruz of only 5 mm 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 ambulacral plates are rather well shown on the figures PL I. 12 13 of Forbes (Monogr. Ech. Brit. 

 Tert), and PL XXVII. 6 7 of L. 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. > (PL 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 may refer to the figures given by Forbes and L. Agassiz and to the 

 one given here (PL XII. Fig. 29) for comparison with the Ech. grandiporus described below. It will be 

 remarked that the radiating supports continue as far as to the peristome; on the abactinal side they only 

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

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



