PHOEMOSOMA HISPIDUM. 



93 



diameter (PI. 40, fig. 3). It differs from the preceding stage by the elonga- 

 tion of the genital plates, the great increase in size of the madreporic 

 genital, and the presence of anal plates intercalated between some of the 

 genitals and oculars. Though this specimen is so much larger than the 

 one just described, the genital openings are not visible ; nor can they be 

 seen in a still larger specimen of 75 mm. (PI. 40, fig. .',). In this there are 

 two anal plates intercalated between the left posterior 

 ocular and the odd genital, and between the right 

 posterior genital and ocular. The other genitals and 

 oculars are separated by a single plate (PL 40. fig. J, ), 

 with the exception of the right and left anterior geni- 

 tals and oculars. 



In specimens 120 mm. in diameter (Pis. 31 ; 33, 

 fig. 3 ; 48, fig. 6), the rows of interambulacral prima- 

 ries on the actinal side are arranged much as in the 

 largest specimens collected ; there are, however, two 

 plates less on the actinal side, so that the second row 

 of primaries is limited to two plates. 



In a somewhat larger specimen 131 mm. in diame- 

 ter (Pis. 35; 30) the primary tubercles are arranged 

 as in the specimen measuring '2(13 mm. The arrange- 

 ment of the miliaries and secondaries in specimens 

 more than 120 mm. in diameter does not differ from 

 that of the larger specimens. Above the ambitus, 

 specimens of 120 mm. in diameter show a greater 

 number of secondary tubercles to each interambulacral 

 plate (PI. 49, fig. 4) than in the oldest specimen, in 

 which the interambulacral plates carry a much greater 

 proportion of miliaries. The ambulacral system (PI. 48, 

 fig. 6') has increased in width ; there are three and two elongated primary 

 plates on the actinal side of the ambitus. Above the ambitus on one side, 

 four of the primary plates are excluded from the interambulacral edge, while 

 on the other — the right when seen from above, Fig. 135 — only two are 

 thus shut off, thus completely changing the position and arrangement of the 

 poriferous zone, the normal arrangement of which is an outer pair of pores 

 with two pairs immediately below, arising from the original linear arrange- 

 ment and the subsequent crowding back of the second ambulacral plate. 



120 mm. 

 Fin. 135. Ph. hispidum. 



