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Show 432 PROF. F. J. BELL ON PONTASTER TENUISPINIS. [May 17, 15 millim. wide at its base, and 7 millim. wide midway between the base and the tip, while an example of " A. tenuispinus," named by the authorities of the Bergen Museum, gives with a base of 15 millim., a width at the middle of the arm of 5-5 millim., or -35 millim. more than would keep the proportions of width of base to width at middle equal in the two specimens. A reference to the diagrams A and B (p. 431), in which the proportions above given are plotted out, will show that in A the " attenuation " is more marked than in B, but the difference is so slight that I submit it is not of the least importance. The original diagnosis goes on " margine alto " ; these words at first presented some difficulty, as several of the specimens before me are remarkable for their flatness; but the matter was quite cleared up when I sent two specimens to Prof. Quennerstedt, in order to have them compared with the type in the University of Lund. These specimens, which I marked A and B, had respectively R = 7 6 and 51, while the depth of the body at the angles was 3'3 and 4-3 millim. each. In A the supero-marginals merely formed a fringe to the upper surface of the arm, while in B they formed a distinct line on the upper surface. In Prof. Quennerstedt's opinion A cannot be A. tenuispinis, while B is certainly very close to it. In other words, A. tenuispinis, as represented by its type, by the figure given by its describers, and by the sketch sent me by the learned Professor of Lund, has the supero-marginals " forming a well-defined border on the abactinal surface." But this is the chief character by which P. limbatus, Sladen, is distinguished from P. tenuispinus, Sladen (D. & K., sp.). As a matter of fact, however, this is a point in which specimens brought from the same locality vary very greatly, and every stage may be found between that in which the supero-marginal is a mere line on the upper surface, and that in which it forms a distinct band. If, however, there are to be specific distinctions made, it is clear that P. limbatus of Sladen must be' regarded as the equivalent of P. tenuispinis, D. & K. ; and P. tenuispinus, Sladen, must receive a new name. For this, however, I see no real need. Recent observers have been struck by the presence at the base of the arm, on the upper surface, of a perforated area, which it has been proposed to call a " papularium," as the tubes which project through the holes are " papular" or respiratory tubes. At times these " papularia " are so distinct that one wonders how it is that they can have escaped the notice of earlier observers ; but the truth is that sometimes the papularia are very indistinct, and at times they cannot be seen at all. This is another very remarkable instance of variation. If the views which I hold are justly derived from the facts which I have cited-facts, I may point out, which any worker during the last ten years might have acquired for himself without any overdue call upon his time-the synonymy of this species may briefly be cited thus :- |
