. Catalogue of casts of fossils, from the principal museums of Europe and America, with short descriptions and illustrations. Fossils. 182 RADIATA. CLASS II.—ACALEPHJE. These soft, gelatinous Kadiates, known as " Jelly-fishes," " Sea- nettles," " Sea-blubbers," " Medusae," etc., vary in size from an al- most invisible dot to a yard in diameter. Large ones often weigh 50 lbs.; yet they are little more, as it were, than " coagulated water," for when dried, nothing is left but a film of membrane, thin as gossamer? and weighing but a few grains. Th
. Catalogue of casts of fossils, from the principal museums of Europe and America, with short descriptions and illustrations. Fossils. 182 RADIATA. CLASS II.—ACALEPHJE. These soft, gelatinous Kadiates, known as " Jelly-fishes," " Sea- nettles," " Sea-blubbers," " Medusae," etc., vary in size from an al- most invisible dot to a yard in diameter. Large ones often weigh 50 lbs.; yet they are little more, as it were, than " coagulated water," for when dried, nothing is left but a film of membrane, thin as gossamer? and weighing but a few grains. The animal is covered by a very delicate epidermis, under which are situated the nettling capsules. There is a distinct muscular system; but the only motion observed consists of an alternate contraction and dilatation of the disc, performed with great regularity about fifteen times a minute. Acalephs have left few traces in stratified deposits, owing to the ex- traordinary softness of their bodies. According to Agassiz, Favosites and Ohsetetes belong to this class ; and it is quite possible, says Dana, that most of the so-called Graptolites are Acalephs. No. 962. Acalepha deperdita, Bey. Two specimens. The remains of this frail creature are circular imprints, composed of very regular concentric circles, on the borders of which are eight rays. These are the only sure remains of a true Acaleph which have been found fossil. From the Lithographic limestone (Middle Oolite\ Eichstadt, Bavaria. Price, $ No. 963. G-raptolithus octobrachiatus, Hall. The Graptolites were first considered of vegetable origin ; subsequently they were re- garded as extremely slender Orthoceratites ; but Portlockhas pointed out their analogy with Sertularia or the lowest forms of Acalephs. They consist of sessile polype cells arranged in one or two rows on flexible, tubular stems which radiate from a central disc. The speci- mens usually observed are fragments of stems in a flattened condition, presenti
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectfossils, bookyear1866
