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BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



the marginal ambulacral tubercles; there are only about 12 of them 

 on the upper plates. Outside the scrobicular tubercles there is 

 another circle of tubercles of about the same size, alternating with 

 the former, and on the median part of the plate still 2 or 3 tubercles 

 medially to the second circle and alternating with them; these last- 

 mentioned tubercles are of the same size as the others. A broad 

 median portion of the plates is left bare and sunken, slightly deepest 

 at the horizontal sutures, representing the usual grooves. At the 

 adradial end of the sutures there is a slight indication of a groove. 

 The median area is about one and one-half times as broad as an 

 areole. 



The apical system (fig. 14) is slightly more than half the horizon- 

 tal diameter of the test. It is flat, scarcely raised around the anal 

 opening. The ocular plates are widely exsert; the line of junction 



of the genital plates is 

 rather conspicuously 

 sunken, the genital plates 

 thus being somewhat ele- 

 vated in the middle. 

 The genital pores (fe- 

 male) are large, nearly 1 

 mm. in diameter, rather 

 distant from the edge. 

 The periproct is small, 

 with few plates. The 

 whole of the apical sys- 

 tem is uniformly, but not 

 very closely, covered with 

 small tubercles of almost 

 equal size; the spines of 

 the apical system also are 

 of almost equal size all 

 over. The tubercles 

 (and spines) are a little more dense around the genital opening. 



The peristome is somewhat smaller than the apical system, and is 

 slightly raised in the form of a cone. There are 8 or 9 ambulacral 

 plates in a series; the ambulacra join at the mouth edge. The inter- 

 radial plates arc 3 or 4 in number. 



The primary spines are only as long as the horizontal diameter of 

 the test. They are comparatively coarse and thick, about 1.5 mm. in 

 diameter, tapering only very slightly and ending in a simple rounded 

 point. In the proximal part they are provided with outstanding, 

 fairly large spinules, arranged quite irregularly, between which the 

 surface is covered with rather coarse, unbranched, not anastomosing 

 hairs (pi. 78, figs. 8, a, b) ; some of the hairs may be thickened, form- 



Fig. 14.— Apical system of Rhopalocibaris hirsutispina (de 

 Meijere), var. viridis, new variety. X8 



