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Show 360 PROF. E. A. MINCHIN ON THE BRITISH [Dec. 13, Since the triradiate systems lie in the wall of a hollow cylinder, the three rays are never in the same plane, but are disposed in such a manner that if the spicule be viewed in a direction corresponding to the axis of the unpaired ray, the two lateral rays appear to meet at an angle less than 180° on the gastral side, greater than 180° on the dermal side. This is an important fact to bear in mind when studying the spicules in preparations. If the spicule be lying on the slide with its dermal face uppermost, then the points of the three rays touch the slide, but their junction is raised off it; hence the spicule appears from this aspect perfectly symmetrical, with two lateral rays of equal length and similar curvature, but each of the three rays is slightly foreshortened. If, on the other hand, the spicule be lying on the slide with its gastral face uppermost it may lie so as to appeal1 symmetrical, but more usually it is found lying with one lateral ray and the posterior ray flat on the slide, the other lateral ray pointing obliquely upwards. Hence when the two rays which lie flat are in focus the third ray is out of focus, and when drawn with the camera it appears foreshortened, giving the spicule an asymmetrical appearance. To this fact is due the foreshortened appearance of one of the two lateral spicule-rays in many of my drawings, especially of L. botryoides, in which the thickened T-shaped triradiate systems are very concave on the gastral face. V. D escription of th e S p ecies. 1. L eucosolenia complicata. Sponqia complicata Montagu, 1812, Wernerian Memoirs, ii. p. 97, pi. ix. figg. 2, 3. Spongici botryoides pars Grant, 1826, Edinb. New Phil. Journ. i. p. 169. Grantia botryoides pars Fleming, 1828, Hist. Brit. Animals, p. 525. Grantia botryoides pars Johnston, 1842, Brit. Spong. and Litho-phytes, p. 178. Leucosolenia contorta pars Bowerbank, 1866, Mon. Brit. Spong. ii. p. 9; 1874, iii. pi. iii. figg. 5-10. Leucosolenia botryoides Gray, 1867, P. Z. S. p. 555. Leucosolenia fabricii O. Schmidt, 1869, Mitth. naturwiss. Ver. Steiermark, ii. p. 91. Leucosolenia fabricii O. Schmidt, 1870, Grundz. Spong.-Faun. Atl. Geb. p. 73. Olynthus hispidus Haeckel, 1870, Jena. Zeitschr. v. p. 237. Olynthus pocillum Haeckel, 1870, 1. c. p. 237. Leucosolenia amceboides Haeckel, 1870, 1. c. p. 243. Leucosolenia (Leucelia) complicata Haeckel, 1870, 1. c. p. 243. Leucosolenia fabricii Haeckel, 1870, 1. c. p. 243. Asculmis seu Ascandra arrnata Haeckel, 1872, Kalkschw pp. 77-79, pi. 13. |