360 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Strongylocentrotus echinoides A. Ag. and Cl. 



Strongylocentrotus echinoides A. Agassiz and Clark, 1907. Bull. M. C. Z., LI, p. 122. 



Plates 94, figs. 13-16; 113, fig. 1. 



This species is so near to drobachiensis that its separation as a distinct species 

 is open to grave doubt, yet when specimens of the same size are compared echi- 

 noides shows certain features that lead one to consider it such. The light color of 

 the test is very noticeable, being more or less reddish white, but specimens of 

 drobachiensis of essentially the same color have been seen. The light green and 

 reddish shades of the spines are quite different from most specimens of drobachien- 

 sis, but this difference is by no means constant. The difference in the granulation 

 of the plates is noticeable, for while in drobachiensis, an abactinal interambula- 

 cral plate may have 50-75 small secondary and miliary tubercles, in echinoides 

 there are twice as many. In the ambulacra, there is an important difference, 

 in that the arcs of pores are less horizontal, the ambulacral plates being corre- 

 spondingly higher and therefore fewer. Thus, in a drobachiensis, with about 

 20 interambulacral plates in each column, there are 35 ambulacral plates, but 

 in an echinoides with 20 interambulacrals, there are only 27 or 28 ambulacrals. 

 The arcs of pores in drobachiensis, in the mid-zone, have 6 pairs, occasionally 7, 

 while in echinoides they have 7, occasionally 6. The poriferous areas are dis- 

 tinctly narrower in echinoides. The primary spines of echinoides are longer and 

 more slender than in most specimens of drobachiensis, but specimens of the latter 

 from Puget Sound cannot be distinguished from echinoides in this respect. 



The pedicellarise of the two species are indistinguishable so far as any char- 

 acters of importance are concerned. In echinoides, the globiferous pedicellarise 

 have valves .40-1.00 mm. in length (PI. 94, figs. 15, 16); the length of the blade 

 is about equal to the width of the base while the length of the terminal tooth is 

 about one half as much. In the tridentate (PI. 94, fig. 13) which vary enormously 

 in size, the valves are .20-2.00 mm. long; in the small ones the valves are narrow 

 and meet for most of their length but in the large ones, the blades are somewhat 

 expanded at the tip and meet only there. In the ophicephalous, the valves 

 (PI. 94, fig. 14) are about half a millimeter long, besides the loop, and are dis- 

 tinctly constricted at base of blade. In the triphyllous, the valves are about 

 .15 mm. long. All these different kinds of pedicellarise are abundant, but the 

 more globiferous there are, the fewer the tridentate and vice-versa. All forms 

 have a neck but on the globiferous it is very short. The spicules show great 



