ACANTHOCIDAEIS HASTIGERA. 39 



faces of the spines. Tlie younger primary spines adjoining tlie abactinal 

 system are not tipped with slioes. They are irregularly triangular, smooth, 

 and pointed (Pis. 38 ; 39 ; 40 ; 41, fig. '2; 42, fig. 5). The abactinal system 

 is pentagonal. The actinal system is smaller than the abactinal. 



Acanthocidaris hastigera A. Ag. and Clark. 

 Plates 11, figs. 1-r,; 12, figs. 1-17; 12 ^ figs. IS, 10; 37-42. 



In a specimen 50 mm. in diameter and 40 nun. in height, the longest 

 abactinal spines measiu-e three times the diameter of the test, the smooth 

 part of the shaft being nearly one quarter the length of the radiole seen 

 from above, and the spines taper very gradually towards the extremity 

 (PI. 38). The extent of the curvature is well shown on two of the longest 

 spines of Pis. 37 and 38, and in PI. 12, fig. 4. The secondary spines (PL 12, 

 figs. 11-14) ''ii'e slender, elongated, flattened, and striated ; they hardly 

 extend beyond the milled ring of the radioles. The miliary spines (PI. 12, 

 fig. 17) resemble the secondaries in every point except in .size, though they 

 appear on the whole as more pointed. The pentagonal abactinal system 

 measures 25 nun. in greatest diameter (PI. 39, fig. 5), while the actinal 

 system does not measure more than IS nun. (PI. 39, fig. 1). There are 

 seven and eight primary tubercles in each vertical interambulacral row; 

 these tubercles are perforate and crenulate. The scrobicular circle is sur- 

 rounded by a single row of large secondaries. The small secondaries and 

 miliaries in two or three irregular rows cover the sides of the interambu- 

 lacral plates, forming a broad, median belt along the suture of the inter- 

 ambulacral plates (PI. 40, figs. /, .'). The scrobicular areas of the small 

 interambulacral plates, near the actinal system, unite on the horizontal line 

 of suture (PI. 39, fig. 1). 



The poriferous zone of the ambulacral area is slightly undulating. The 

 area itself is divided into three belts of equal width ; the two poriferous 

 zones and the median ambulacral belt which is defined by a vertical line of 

 small secondaries flanking the poriferous zones (Ph 40, fig. 1), with a line of 

 minute miliaries on the median angle of each ambulacral plate. The larger 

 ambulacral tubercles carry comparatively long, slender, sharp-pointed spines. 

 The miliary spines are slender and minute. The outer line of pores is com- 

 posed of larger pores than the iuner line; the pores are slightly confluent. 



The genital plates are irregularly hexagonal with rounded angles, the 



