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Show 510 . PROF. F. J. BELL ON THE GENUS ASTERIAS. [May 3, to examine the proportion between the greater radius and the width of the base of the arm. The absolute measurements have already been given; these, when worked out, give the following proportions :- A. hispida--2-1, 2*16, 2*18, 2*20, 2*4, 2*419, 2*5, 2*6, 2*83, 2*85, 30, 3*4; A. ruBens-3-0, 3*06, 3*25, 3*28, 3*50, 3*6. It is, then, so far clear that the base of the arms is wider in A. hispida than in A. ruBens for specimens of, or about, the same size. When we measure larger specimens of the commoner species, we find the proportional value of the base of the arm to be 2*62, 2*86, 3*45, and 3*76. And this series falls in as well with A. hispida as with A. ruBens; there is, however, this essential difference-that, in the former, 22 varies between 19*5 and 7'5 millim., while in the case of A. ruBens B has the minimum value of 42 millim., and a maximum value of 64 millim. After all, however, it is hardly necessary to raise the question of proportions ; for A. hispida would seem to have never more than one row of adambulacral spines, whereas A. ruBens has frequently two ; and, in the second place, there are absent from it the larger pincer-formed " pedicellariae." Now arises an important and difficult question,-Is the absence of these pedicellariae any thing more than a specific characteristic 1 In other words, should it not be regarded as a mark of generic difference. Sufficient information is not yet at hand to justify any final decision; but I would suggest that the question be kept before the minds of naturalists who busy themselves with these difficult forms. I am myself inclined to believe that there is only a tendency to their complete disappearance, and that the difference is purely specific. On the other hand, we know far too little as to the conditions of existence under which these creatures live. Is it not possible that, after all, A. hispida is but a pure variety, or a local race, or a form stunted by living under disadvantageous conditions l. It is, indeed, possible; but, at present, the weight of evidence is in favour of Forbes's original position, that A. hispida is a distinct species. (2) Characters of A. muelleri, Sars. The collection of the British Museum contains two specimens bearing the "etiquette " of A. muelleri. One, in spirit, was named by Dr. Liitken, and it may therefore be regarded as a good, though, of course, not by any means necessarily a "typical" specimen of the species; the other, which is dried, bears a label " Asterocanthion (sic) miilleri:" it was "purchased of Brandt;" but there is no evidence as to who named it. The specimen named by Dr. Liitken has 22 equal to 13 millim., while r=3, and the breadth of the arms at their base is 3*5 millim. 1 Compare especially the interesting remarks of Prof. Eupert Jones in bis very philosophical paper on Variation in the Foraniinifera (Monthly Micr. Journ. 1876 pp. 61-92) |