SALENIA MILIARIS. 47 



The scrobicular areas of the primary tubercles are already connected 

 in specimens 10 mm. in diameter ; in younger specimens the areas of the 

 principal plates are still isolated (PL 17, figs. 4,-6). The scrobicular areas 

 (PI. 19, fig. 3) of the larger primary tubercles are flanked on each side 

 by five to six secondaries with one or two miliaries in the narrow .space 

 between these and the ambulacra (PI. 18, figs. S, 0), while in the wide 

 median interambulacral area the miliaries are more numerous. The larger 

 primary tubercles are crenulated, but those nearer the actinal system 

 are not. 



The radial and concentric mode of growth of the coronal plates is well 

 shown in PI. 19, figs. 3, 4, 5 ; figs, i and 5 illustrate specially the inde- 

 pendent growth of the interambulacral and ambulacral plates by the 



Fig. 78. Salenia v.4.kispina. 



gradual intercalation of additional calcareous material in the connecting 

 angles of the plates. In fig. 5 there are five ambulacral on the side of 

 the interambulacral plate, while there are only three and two halves in 

 fig. 4' Towards the actinal edge. Fig. 78, the sutures of the actinal inter- 

 ambulacral coronal plates are somewhat curved, the sloping plates con- 

 trasting greatly to the rectangular plates which follow (PI. 16, fig. J). 



In all the SalenijB thus far known the actinal system (PI. 19, fig. 1) is 

 covered by small elongated imbricating plates irregularly arranged occupy- 

 ing the whole space between the ten ambulacral buccal plates and the 

 coronal plates. In young specimens the ten ambulacral buccal plates 

 occupy the greater part of the actinal sj^stem (PL 16, fig. 1). With increas- 

 ing age the buccal plates become larger (PL 16, figs. 3. 5), and the other 

 actinal plates increase greatly in number, though without showing any 

 regular arrangement (PL 17, fig. 1). In Salenia miUaris the actinal plates 

 show but little trace of imbrication. The ratio between the actinal system 

 and the diameter of the test does not change with age, Fig. 79 ; in 



