104 PANAMIC DEEP SEA ECHINI. 



The buccal plates of Ph. panamem:e are in striking contrast with tliose 

 of Ph. hispidiim ; the former are narrow elongate, Fig. 147, as compared 

 with the broad, high, ambulacral buccal plates of the latter. 



Above the ambitus, Fig. 148, the greater number of the large ambulacral 

 plates are excluded from the outer edge ; this is formed by the larger of 

 the smaller ambulacral plates. The inner poriferous plates are small, 

 triangular, and separated by a tongue of the larger excluded primary ambu- 

 lacral plate. In a Ph. hispidum of about the same size not more than five 

 or six primary ambulacral plates above the ambitus are thus excluded from 

 the outer edge ; in Ph. panamense there are from nineteen to twenty. 



There is no species of Phormosoma which shows 1o such an extent the 

 splitting up of the primary plates both in the ambulacral and interambula- 



130 mm. 



Fio. 149. Phormosoma paxamense. 



oral areas. While this can be seen to a certain extent from the exterior 

 by the fine irregular lines crossing tlie primary plates, in Fig. 148, in all 

 directions, it is best seen from the interior. Fig. 149, where the secondary 

 plates lap more or less and their edges ar.e raised. The splitting up extends 

 to the larger secondary ambulacral plates. 



The abactinal system of Ph. pauamoise, Fig. 150, is marked for the 

 elongated outline of the ocular plates, which in Ph. hispidiim are quite 

 pentagonal. The genital plates are also smaller than those o^ Ph. hi^pidum, 

 and the genital pore is placed in the upper part of a narrow membraneous 

 slit which separates the second or third interaml)ulacral plates. The madre- 

 poric genital exceeds greatly in si/.e thi' other genitals, and the madreporite 

 extends over two of tlie adjoining anal plates. 



There are from three to four concentric rows of small polygonal anal 

 plates carrying from one to two miiiarios according to the size of the plates. 



