Page:Scientific results HMS Challenger vol 18 part 2.djvu/282

1158 The Phænocalpida are probably an artificial family, composed of three or four (or perhaps more) different groups, which have a quite different origin. The Litharachnida (genera 511-515) and the Haliphormida (genera 516-518) are probably derived from the Sethophormida by loss of the cephalis, the retrograde metamorphosis of which may be observed in all its different stages. The Halicalyptrida (genera 519-521) are perhaps independent of the other Phænocalpida, and may be Archicorida which have produced a corona of teeth around the mouth, without relation to lost radial ribs. The Phænoscenida (Phænocalpis, Phænoscenium) may be derived from the Euscenida (genera 504-507) by interpolation of interradial feet between the three primary ones, or directly from the. The Calpophænida, on the other hand (Calpophæna, Archiphæna), may have arisen from the Zygospyrida (Petalospyris, Gorgospyris) by loss of the sagittal ring and the longitudinal constriction. The phylogeny of the Phænocalpida is therefore a very complicated problem, as yet unsolved.