. The Cambridge natural history. Zoology; Zoologia Geral. YIH FOSSIL HEXACTINELLIDA 2O7 Fossil Hexactinellida. This has the distinction of including among its. group Lyssacine members the oldest known sponge, Protospongia fenes- trata, of Cambrian age (Salter). As preserved it consists of a single layer of quadriradiate, or possibly quinqueradiate spicules, which, arranged as a square meshed lattice, supported the superficial layer of the sponge (Fig. 101). Whether or not the fossil represents the whole of the sponge-skeleton does not The extraordinary Recepta- culitidae are probably
. The Cambridge natural history. Zoology; Zoologia Geral. YIH FOSSIL HEXACTINELLIDA 2O7 Fossil Hexactinellida. This has the distinction of including among its. group Lyssacine members the oldest known sponge, Protospongia fenes- trata, of Cambrian age (Salter). As preserved it consists of a single layer of quadriradiate, or possibly quinqueradiate spicules, which, arranged as a square meshed lattice, supported the superficial layer of the sponge (Fig. 101). Whether or not the fossil represents the whole of the sponge-skeleton does not The extraordinary Recepta- culitidae are probably early Lyssacine forms : they are cup- or saucer-shaped fossils, abundant in FIG. 10L— Part of the specimen of Pro- . tospongia fe .Silurian and above all in Devonian * strata, and have been " assigned in turn to pine cones, Foramini- fera, Sponges, Corals, Cystideans," and Tunicata. Hinde' brings forward im- portant arguments for retaining them among Hexactinellida. The only elements in the skeleton of the simpler genera, Ischaditcs, are structures comparable to Hexactinellid spicules. The surface of the fossil presents a series of lozenges FIG. 102. -A portion of the forming a regular mosaic. Each lozenge outer surface of a Recepta- -[s the expanded end of one of the rays culitid. Acanthoconia bar- . , „ which the ex- ol a spicule ; it conceals tour rays in one nestrata in the Sedgwick Museum, Cambridge. Nat. size. (After Soiias.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harmer, S. F. (Sidney Frederic), Sir, 1862-; Shipley, A. E. (Arthur Everett), Sir, 1861-1927. [London, Macmillan and co. , limited; New York, The Macmillan company
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