REPORT ON THE HEXACTINELLIDA. 63 



end into a very irregular network with large meshes, so that a labyrinth of hollow spaces 

 is formed. Among the isolated siliceous spicules, in addition to the well-known 

 Euplectella-&OTicome&, the branches of whose rays have a very fine basal portion and an 

 unbent plate with a toothed margin at the extremity, 0. Schmidt found rosettes with fine 

 hook-like teeth, or with terminal umbels bearing four or more prongs, and other forms 

 in which each of the six principal rays runs out into five teeth which bear on their 

 extremities hemispherical discs with numerous strong, recurved, marginal rays. Of these 

 five teeth with their terminal discs, the middle one is always distinctly smaller than the 

 four surrounding it. A remarkable spiral bow-shaped spicule with transverse furrows is 

 also mentioned by 0. Schmidt, and finally the presence of many rayed stars is noted. 



A small sponge with similar siliceous parts, but consisting merely of a simple tube 

 open above, with a loose stalk, and a basal plate which resolves itself at the margin into 

 spicules and spicular bundles, is described by 0. Schmidt as a young Rhahdopectella 

 tintinnus, and he has accordingly conjectured that the larger (older) specimens are only 

 the upper portions of similar tubes which had been lost in the dredge. 



The first reports of fossd Euplectellidse have been made during the last few yeai-s. 

 R. P. Witefield ^ first drew attention to the fact that the structures which were described 

 from the Chemung group of New York, the Waverley beds of Ohio and of several other 

 places, under the name of Dictyophyton, and which were mentioned in the Sixteenth 

 Repoi't of the State Cabinet of Natural History of New York, p. 84, as "algse of a peculiar 

 form and mode of growth," present a certain resemblance to Euplectellid skeletons, since 

 in the wall of the tube longitudinal and transverse bands of fibres are seen to be united 

 into a network with rectangular meshes. Soon after, Witefield '■ confirmed this view in 

 greater detail, and supported it by reference to a Uj^hantwnia dawsoni, which had been 

 described by T. W. Dawson, pointing out that the beams of the rectangular network 

 consist of "fascicles of slender cylindrical rods or spicules, quite cylindrical and smooth," 

 and that the " spaces between the bands and threads are covered by a thin fibre, which 

 is alternately elevated or depressed in the adjoining spaces." 



By this communication of Witefield, Walcott^ was induced after closer examination to 

 announce, as a fossil Euplectellid, an organism which he had formerly described, under 

 the name of Cyathophycus, as a fossil Alga, of a tube-like form, and with an enveloping 

 coat of retiform structure. He described "horizontal and perpendicular series of narrow 

 bands crossing each other at right angles, so as to form a network with rectangular 

 interspaces, the narrow bands being formed of thread-like spicula resting on or one 

 against the other." Of the form described as Cyathophycus, Walcott said: — "The 

 striking resemblance to UuplectcUa is seen at a glance, although the convex summit of 



1 Aracr. Joum. Sci. and Arts, July 1881; Aim. and Mag. Nat. Hist., ser. 5, vol. viii. p. 167. 



2 Amer. Joum. Sci. and Arts, August 1881; Aim. and Mag. Nat. Hist., ser. 5, vol viii. p. 237. 



3 Amer. Joum. Sci. and Arts, 1881, vol. xiii. p. 394, 395. 



