288 TEMNECHINUS MACULATUS. 



structure and coloration of the fusiform spines to show their connection. The 

 test denuded and magnified presents the peculiar hub-shaped arrangement of 

 the ridge to form the secondary tubercles round the base of the primaries (PL 

 VI II. f. 1J,). When somewhat older the actinostome is much smaller (Pi. 

 VIII. f. 15), slightly angular, the genital plates not yet distinctly formed. 

 In the following stage (PL VIII. f. 8, 9), the pits at the base of the tubercles 

 are quite marked | /'/. VIII. f. n), the spines are about a third the diameter 

 of the test, but have quite the general aspect of those of larger specimens 

 (PL VIII f. 12). The abactinal system is well formed, the genital plates 

 rising above the level of test, are pentagonal, deeply grooved for the opening 

 of the genital openings, the madreporic body prominent (PL VIII. f. 10), 

 and a single conical plate fills the whole of the anal system. The auricles 

 resemble those of some species of Temnopleurus (PI. VIII. f. IS). 



The largest specimens collected (Pi. VIII. f. 1, J f ) have the same structure 

 in the middle of test which is found in the youngest plates of Temnechinus, 

 showing that eventually these incipient pits will fall together, forming pits 

 similar to those of the fossil species (PL VI I If. ,;o). The outline of the test 

 is regularly arched, slightly flattened at top (PL VIII. f. 7). The changes in 

 the poriferous zone are slight, the zone of the older specimens being some- 

 what undulating (PL VIII. f. >,) or angular, while in younger specimens the 

 poriferous zone is vertical (PL VIII. f. i.' t ); the ridges separating the pairs 



of pores becoming more distinct with age, and the pores more sunken. 

 From 30 to 1G0 fathoms. 



Among the Temnopleuridae the changes due to growth are very promi- 

 nent ; hence the difficulty of recognizing the species thus far established, as 

 the descriptions belong to specimens not identical in age. It would be 

 hardly possible to recognize in PL VIII. f. ,.'.' and PI. VIII. /'. .' ; corre- 

 sponding portions of the test of Temnopleurus Reynaudi ; the sharp, deep, 

 rectangular pits at the sutures of the plates (PL VIII. f. .",). taken with the 

 peculiar anal system of this stage of growth (PI. VIII f. .'■!). with its large 

 elliptical anal plate covering nearly the whole anal system, would certainly 

 warrant us in separating these specimens from those with wide, diffuse, tri- 

 angular depressions at the sutures of the plates (PL VIII. f. .'.'), having promi- 

 nent, isolated, comma-shaped secondaries round the primary tubercles, and an 

 anal system in which, although one plate is much more prominent than the 

 others, yet is relatively small compared to the size of the anal system 

 (Pi VIII. f. 2 '/). 



