114 PANAMIC DEEP SEA ECHINI. 



the ambitus of the bare spaces separating- the interambulacral plates (PI. 51, 

 figs. •'. 7), while on the abactinal side the calcified parts of the coronal 

 plates are still united along the whole length of the sutures (PI. 51. 

 figs. 6, /'). In this specimen there are five and six rows of actinal plates 

 (PI. 51, fig. ■'>), leaving a narrow hare belt next to the coronal plates partly 

 filled in the interambulacral area with small very narrow elongate calcareous 

 plates. The buccal plates are edged with a horizontal actinal row of from 

 three to five large miliaries. The primordial interambulacral plates have 

 already heen somewhat reduced in size by the resorption of their actinal 

 edge (PI. 51, fig. .7). A number of spheridia are shown on the actinal sur- 

 face of the ambulacra. 



In the genital ring the genital plates are polygonal, larger than the 

 oculars (PI. 51, fig. 6), which are more elongate toward the anal system ; 

 their distal extremity narrows to a rectangular outline; it extends no 

 farther along the interambulacral plates than do the genitals. The madre- 

 poric genital is larger than the others, the madreporite occupies a part 

 of the centre of the plate ; the madreporic and the odd posterior genital 

 are perforated by a large genital pore. The plates of the genital ring 

 are nearly bare ; they carry only one small secondary and one to two 

 small miliaries placed in the anal part of the plates. The anal system 

 is polygonal, with one outer row of well marked larger plates of irregular 

 shape enclosing an inner space filled with much smaller elongate plates. 

 The larger plates carry a single secondary or miliary tubercle and sometimes 

 a second smaller miliary. The genital ring is closed. 



In this specimen there are nine interambulacral plates between the 

 actinal system and the ambitus and twelve between it and the genital ring 

 (PL 51, fig. 7). The abactinal part of the ambulacra! zone (PI. 51, figs. /. 

 13) clearly shows the small primary ambulacral plates adjoining the oculars, 

 their crowding from the outer edge of the second and third pair of pores 

 toward the median line (PI. 51, figs. /.', 13), and finally their exclusion from 

 the outer edge (PI. 51, figs. 10, II) in the third or fourth plate above the 

 ambitus, and their position inside of the pores of the large primary plate, 

 until near the actinal system the pairs of pores again reach the outer edge 

 (PI. 51, fig. 9). 



The tentacles at the coronal edge of the actinal system have no well 

 developed disk. The tuberculation of the plates of the ambulacral system 

 is quite prominent on the two sides of the test near the ambitus, where the 



