A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) . dina: a,Mastosia. Anomocladina : b, Cylindjophyma. Tetracladina : c, d,Callopegma; e, Plinthosella. e, enlarged 26 diam.; the rest 40 diam.(After Hinde.) cladina (Fig, 13 &); Cylindrophyma is common in UpperJurassic rocks. Megamorina (Silurian to Eecent) : desmasrelatively large, curved, branching rods, either intertwiningor joined as in Eutaxicladina (Fig. 12 e, f, g)\ Doryderma(Fig. 16 &) is abundant in the Upper Chalk. Rhizomorina(Cambrian to Eecent) : desma sm
A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) . dina: a,Mastosia. Anomocladina : b, Cylindjophyma. Tetracladina : c, d,Callopegma; e, Plinthosella. e, enlarged 26 diam.; the rest 40 diam.(After Hinde.) cladina (Fig, 13 &); Cylindrophyma is common in UpperJurassic rocks. Megamorina (Silurian to Eecent) : desmasrelatively large, curved, branching rods, either intertwiningor joined as in Eutaxicladina (Fig. 12 e, f, g)\ Doryderma(Fig. 16 &) is abundant in the Upper Chalk. Rhizomorina(Cambrian to Eecent) : desma small, usually elongate, curved,with irregular branches; these end in minute facets, which 38 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. Gallery X. are closely apposed to the axis and branches of adjoiningspicules so as to form loosely arranged fibres or an irregularmeshwork (Fig. 12 a, h); the Cretaceous Verruculina(Fig. 17) is characteristic. Sub-Class II. — monactinellida. Demospongiaewith monaxon spicules. The chief modifications of this simple type of spiculeare shown in the accompanying figure (Fig. 14 a-q). With. Fig. 14.—Fossil sponge spicules : Silicispongiae, Monactinellida. a-q areskeletal, r, s, t are flesh-spicules. An open axial canal is shown in /;a closed canal in g. a, e, enlarged 26 diam.; 6, 100 diam.; c, f, g, i, j,k, q, 40 diam.; d, 66 diam.; li, m, n, o, r, s, t, li4 diam. , I, p, 13 diam.(After Hinde.) these are associated smaller flesh-spicules, serving as grapnelsin those forms that have a harder outer skin or cortex(Fig. 14 r, s, t). In these latter, constituting the OrderHadromerina or Spintharophora, the spicules are looselyand irregularly arranged. In the other Order, Halichon-drina^ the siliceous spicules are bound into a skeleton bythe horny substance spongin. Consequently, though thespicules abound in siliceous deposits, chiefly of Tertiary age. Table-cases complete sponges are rarely preserved. Clmlina, Beniera,15, 14. and the freshwater Spongi
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Keywords: ., bookauthorbr, bookcentury1900, bookdecade1900, booksubjectfossils
