File:The Cambridge natural history (1895) (20769161005).jpg

Title: The Cambridge natural history
Identifier: cu31924024535431 (find matches)
Year: 1895 (1890s)
Authors: Harmer, S. F. (Sidney Frederic), Sir, 1862- ed; Shipley, A. E. (Arthur Everett), Sir, 1861-1927. ed
Subjects: Zoology
Publisher: (London, Macmillan and Co. , Limited; New York, The Macmillan Company
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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FOSSIL HEXACTINELLIDA 207
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Fossil Hexactinellida. This group has the distinction of including among its 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 appear.^ The extraordinary Recepta- culitidae are probably early Lyssacine forms: they are cup- or saucer-shaped fossils, abundant in Fig- 101.âPart of the specimen of Pn- aâ¢^ ⢠J 1. n ⢠-r. â tospongia fenestrata m the Sidawiok Silurian and above all m Devonian Museum, Cambridge. Nat. size. strata, and have been " assigned (,^it&t Soiias.) 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, e.g. Ischadites, are structures comparable to Hexactinellid spicules. The surface of the fossil presents a series of lozenges Fio. 102.âA portion of the forming a regular mosaic. Each lozenge outer surface of a Recepta- fg the expanded end of one of the rays culitid, Acanthoeoma oar- . . , . t i. . randei, in which the ex- 01 a Spicule; it conceals lour rays m one panded outer rays of the pi^ne, tangential to the wall of the cup- spicules are partially de- â »⢠o j. stroyed, revealing the four shaped fossil, while the sixth ray pro- tangentiai^^jays^^beneath. ^^^^^ vertically to the Wall into the cavity of the cup. In the genus Eece2itaculites itself there is an inner layer of plates abutting against the inner 1 Sollas, Quart. Journ. Geol. Soc. 1880, p. 362.' ^ Quart. Journ. Geol. Soc. xl. 1884, p. 795.

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