HABEOCIDARIS ARGENTEA. 79 



pentagonal, somewhat more markedly so in II. argentea (PI. 54, fig. 2). It is 

 but sparsely covered with small, sesssile granules which become somewhat 

 club-shaped on the three upper abactinal plates of each interambulacrum. 

 There are five anal plates. The genital plates are elongated, each with one 

 small genital pore. The pore of the madreporic genital is somewhat larger 

 and placed nearer the centre of the plate than in the other genitals where it 

 is close to the anal system. 



There are only five primary interambulacral plates (PI. 54, fig. 3) on each 

 side of the median line above the large, odd, primary interambulacral plate. 

 This is irregularly heptagonal, elongate with concave lateral sides and a 

 broad actinal base slightly indented ; it carries one small primary tubercle in 

 the centre of the plate (PI. 54, fig. 1). This plate separates the next pair of 

 ventral interambulacral plates, each of which has a single primary tubercle 

 near the upper suture. The next pair of plates join along the median line, 

 and each carries a large primary tubercle close to the ambulacral edge of the 

 plates. Riding across the median suture is a large primary tubercle, above 

 which the interambulacral plates bear only minute, scattered, somewhat 

 club-shaped granulations (PI. 54, figs. 2, 3). 



In the ambulacral areas (PL 54, figs. /, 2) the first four or five pairs of 

 plates are narrow with a slight pit near the sutures, carrying the pores. A 

 similar depression in the median line in the angles of the first two pairs of 

 ambulacral plates contains the sphaeridium. The next three plates each carry 

 near the centre a primary tubercle, the largest of which is on the upper plate. 

 The pores of these and the six or seven small primitive plates are not in pits, 

 each pair of pores with one exception in the angle of each plate (PI. 54, fig. 2). 

 On each of these upper plates there are but two or three minute granules. 



The tridentate pedicellarioe are rare and occur only near the ambitus. 

 The valves (PL 49, fig. H) are about .38 mm. long, narrower than in scutata, 

 more rounded at the tip, and the branches of the apophysis nearly reach the 

 margins of the valve. 



The ophicephalous pedicellarioe are abundant abactinally and have very 

 long stalks. The valves (PL 49, figs. 12 and 13) are about .28 mm. long, much 

 narrower and more slender than in scutata, but of the same general pattern. 

 The upper end of the stalk (PL 49, fig. 10) is slightly different. 



The triphyllous pedicellarise are apparently wanting. 



The calcareous deposits in the pedicels (PL 49, fig. 11) are similar to those 

 in scutafa, but are smaller and more slender. 



