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Show 376 PROF. E. A. MINCHIN ON THE BRITISH [Dec. 13, Haeckel lias given a plate (Monographic, pi. 18) intended to represent the form-variations of L. variabilis, but, in my opinion, the greater number of his figures are untrue to nature. The most charitable interpretation that can be put upon this plate is to suppose that many of the specimens figured are incorrectly determined and are not L. variabilis at all. Thus fig. 12 is evidently a Clathrina, and fig. 15 is either a contracted Clathrina, probably coriacea, or possibly a specimen of variabilis in which, owing to rough usage, all the oscular tubes have been knocked off. Fig. 2 probably represents some of the Sycons which, as I have stated below, are commonly found growing in company with L. variabilis, and the same interpretation possibly applies to figg. 1 and 3, the latter being contracted ; what figg. 10 and 13 may be I should not like to assert, but they are certainly not specimens of variabilis. On the other hand, figg. 8 and 14 are probably specimens of variabilis, which owe the extraordinary curves exhibited by their oscular tubes to shrinkage as the result of desiccation. The imaginative figures given by Haeckel on this and other plates are responsible for the general opinion, far from being true, that any Ascon may assume any form in which any other species of Ascon occurs. As compared with other species, I find a tendency in variabilis for the oscular rim to be of greater length. In young specimens this is sometimes very marked indeed. The body-wall of variabilis is generally thicker and stronger than in L. complicata, and the sponge is evidently hardier, as seen from the more exposed situations in which it grows. (a) Triradiate and Quadriradiate Systems.-(1) The ordinary triradiates (text-fig. 94, figg. 10 a-10 c, &c., p. 377) have the rays slender or of moderate thickness and tapering gradually to sharp points. The unpaired ray is straight, and distinctly shorter than, very rarely as long as, the paired rays. The unpaired angle is always much greater than 120°. The paired rays usually show a distinct double curvature, each ray curving first backwards, then forwards (b) Characters of the Spiculation. Explanation of Text-fig. 94 (opposite). Spicules of Leucosolenia variabilis. F igg. 1 0 « - 1 0 « . Sllicnles o f a Kno<>iinon nn+Vi --- ____________ |