. Smithsonian miscellaneous collections . ndi-vidual spicules appear to have been united by sarcode or held in afine spicular film and not cemented together by a siliceous osculum has short spines about it and there may be a greatdevelopment of protective dermal spines. The rays of the large bodyspicules taper gradually from the central body to their pointedextremities; the rays of the smaller spicules and the slender dermal 1 Trans. Royal Soc. Canada, 2d ser., Vol. 2, Sec. IV, 1896, pp. 101-106. NO. 6 MIDDLE CAMBRIAN SPONGIAE 303 and protective spicules appear to be nearly cylindri
. Smithsonian miscellaneous collections . ndi-vidual spicules appear to have been united by sarcode or held in afine spicular film and not cemented together by a siliceous osculum has short spines about it and there may be a greatdevelopment of protective dermal spines. The rays of the large bodyspicules taper gradually from the central body to their pointedextremities; the rays of the smaller spicules and the slender dermal 1 Trans. Royal Soc. Canada, 2d ser., Vol. 2, Sec. IV, 1896, pp. 101-106. NO. 6 MIDDLE CAMBRIAN SPONGIAE 303 and protective spicules appear to be nearly cylindrical. The anchor-ing rods or spicules vary from the single rod of P. mononema to thefour rods of P. tetrancma. The latter are slender, filiform, cylin-drical rods, pointed at both ends, with their proximal ends insertedapparently in the basal part of the body of the sponge ; the anchoringrod of P. mononema is described as having from two to four shortspreading branches at the base or a single elongated anchor-shapedspicule with fine **x Fig. 5.—Protospongia mono-nema. Restored. Fig. 6. -Protospongia mononema. Cruciformand protective spicules, X 5- The presence of a dermal membrane is indicated in many speci-mens by a rusty brown covering of minute pyrite crystals. The studies of Dawson and Hinde indicate that Protospongia isthe simplest known form of the Hexactinellida and its occurrencein the Lower Cambrian proves it to be one of the earliest sponges yetknown from Cambrian strata. The spicules from the Lower Cam-brian 1 are apparently identical with those from the Middle Cambrianof Wales. Dawson gives diagrammatic figures of two species of the genus,one of which is reproduced here for comparison with the Burgessshale species and as illustrating the 1 Tenth Annual Rept. U. S. Geol. Survey, 1890, p. 597, pi. XLIX, fig. 2. 2 Trans. Royal Soc. Canada, Vol. VII, Sec. IV, 1889, p. 40, figs. 5 and 6. 304 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 61/ The spicules refe
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