62 THE VOYAGE OF H.M.S. CHALLENGER. 



Arbacia of the east coast of the United States that it was intended to replace the 

 wear of the tip of the spines in moving about, a use to which the huge curved spines 

 of this genus, placed as they are above the ambitus, can hardly have been put, unless 

 possibly to raise the test high above the bottom and keep it in suspension ; this, however, 

 is probably not a common use of these radioles of the abactinal surface as although 

 slightly worn they are not sufficiently reduced to show extensive usage. 



There are no notes with these specimens on their movements after they are brought 

 up in the dredge.^ We find as in all Arbacice the round-headed pedicellarise (PL VI. figs. 

 17, 18) occurring near the abactinal region, while the large-headed, triangular, long- 

 stemmed pedicellarise (PL VI. fig. 16) are found along the test towards the ambitus and 

 more abundantly near the edge of the actinal membrane. The large plates of the actinal 

 membrane are covered by numerous short-stemmed round-headed pediceUarise (PL V. 

 fig. 2). The colour of the base of the shaft of the primary radioles is brownish, of the 

 secondary spines many are of the same colour, but as many are of a brilliant carmine, 

 the white part of the primary shaft, its shoe, is often banded longitudinally with brilliant 

 vermilion or with rectangular spots of the same colour on the upper part of the shaft. 

 In large specimens only here and there a coloured primary spine is found, while in young 

 or smaller specimens the spines are nearly all brilliantly coloured (PL V. fig. 3), the 

 glistening white shaft of the large specimens being usually of a delicate pea-green colour, 

 which is well set off by the longitudinal bands or the spots of IjrilUant vermilion along 

 the shoe, the base of the shaft being a dark greenish-brown or red. In these specimens 

 the short flat spines near the actinal area are frequently banded and spotted like the larger 

 ones. In small specimens the secondary spines are all coloured (PL V. fig. 3), and near 

 the abactinal surface they are more or less club-shaped (PL VI. figs. 20, 2\d), much like 

 the iTidimentary temporary spines of the abactinal region of the Arbaciadse, only they are 

 articulated and not soldered to the test as is the case in the other genera of this family. 



In a specimen measuring 41 mm. in diameter, the width of the ambulacral system 

 (PL VI. fig. 7) near the ambitus is as great as that of the interambulacral. In 

 the former there are twelve primary tubercles increasing rapidly in size from the 

 actinal opening towards the edge of the test, where there follow three to four very 

 prominent tubercles, which are again followed by smaller tubercles rapidly decreasing in 

 size and extending to the genital ring (PL VI. figs. 1-3, 5, 7). The scrobicular circles are 

 large, and adjoining primary tubercles are separated in the median ambulacral space by 



' Quite a number of specmieiis of Ccslophurus floridanus, A. Agassiz, were dreclgeJ during the season of 1878-79 

 liy the " Blake." On placing them in a pail of water I found that they used their large spines as indicated above merely 

 to raise themselves otf the bottom when distm-bed, using the shorter, stouter tipped spines of the actinal surface for 

 locomotion much as the common Arbacia pitstulosa of the east coast of the United States. Their movements, however, 

 were jnuch slower than those of Arbacia jm^tulosa, which moves rapidly (see Revision of the Echini). The coloiu- of the 

 West India CcclopleHrus is quite well kept in alcohol, and I presume the same is the case for the Ccclopleurus collected 

 l>y the Oliallenger. ^vhich show like the Florida species a great range and beauty of coloration. 



