OCR Text |
Show 434 PROF. F. J. B E L L O N A N E W SPECIES O F MESPILIA. [Mar. 15, special point which characterizes this new species will perhaps into prominence the whole question of the real affinities of these forms: it is the well-marked character of the gill-cuts of the actinostome, which, in the only species of the genus known hitherto, are so very feebly developed. The specimen on which the following description is based was presented by the Rev. S. J. Whitmee, and is stated to have come from the Samoa Islands. It is in the dry condition. The test, from above, is obscurely pentagonal in form, and not at all high; the spines are delicate, yellowish or greenish yellow in ground-colour, and banded or tipped with red; they are richly developed over the whole surface of the test, with the exception of the middle portion of the interambulacral arese. In correspondence with this there is, of course, a portion of the interambulacral plates devoid of primary tubercles; but this is only seen above the ambitus ; this bare band is much narrower than in M. gloBulus. At the ambitus there are four large primary tubercles in a row on either side of the middle line ; the space on either side of these is occupied by smaller tubercles, which are not quite so regularly arranged ; as we pass nearer the actinostome, first these latter tubercles and then the outer primary tubercles disappear; those that remain retain or even exceed the size of those at the ambitus. In the ambulacral arese a row of four tubercles on either side can likewise be made out at the ambitus. In having the same number of primary tubercles in the interambulacral as in the ambulacral area this species differs from M. globulus, which, however, it resembles in having the largest and most conspicuous of the interambulacral tubercles nearest to the poriferous zone. There is but a very feebly developed, bare, intraambulacral space; but the sutural pores between the plates are more conspicuous in the ambulacral than in the interambulacral arese. The gill-cuts are well marked and wide. The auricular foramen is large, much larger than in M. globulus, and quite as large as, if not larger than, that of AmBlypneustes pallidas. The connecting ridge is low, and, at its middle point, is produced into a short, pointed, upwardly-directed process ; the actinostome is moderately large. The abactinal area is by no means small; all the oculars remain shut out from the edge of the anal area; and in no essential point does it differ in character from that of M. gloBulus ; there is a rich supply of tubercles; and the peripheral anal plates are large and tuberculated. The poriferous zone is not so wide as in M. gloBulus ; but the pairs of pores are still arranged in two vertical rows, and the number of those in the outer seems to be about double those in the inner row. The foramen of the pyramid is perhaps a little larger than in M. gloBulus; as in it, the radius is not bifid at its free end ; but its spatulate character is very much more developed. The general ground-colour of the test is greyish brown; the tubercles are yellowish or whitish. |