Volltext Seite (XML)
ZoOPHYTA.] LOWER PALAEOZOIC RADIATA. IS space of one line; upper and under surface of slightly weathered specimens shewing vertical, vermicular perforations about one-fourth of a line in diameter, passing nearly at right angles through the numerous layers composing the mass, at distances varying from one to two lines apart. This exclusively Silurian species has been confounded with the exclusively Devonian Stromatopora con- centrica of Goklfuss by Mr Lonsdale (Silurian System, &c.), and by Prof. Phillips (Palaeozoic Fossils, Memoirs of the Geological Survey, Yol. II. &c.) but has been briefly distinguished by d’Orbigny, in his recent “Pro drome,” on account of the greatly fewer number of the layers in a given space, and more delicate nature of the reticulation; a conclusion to which I had independently come before receiving his volume, using the same character as an easy mode of distinguishing the Stromatopora of Newton Bushell (Devonian) limestone from that of the Silurian limestone of Wenlock. It may be well to state that I derive my notion of the true S. concentrica of Goldfuss from authentic specimens from the Eifel. One specimen, partially weathered, from the Wenlock limestone of Wenlock edge, shews most clearly on its upper and under surfaces and crossing the vertical edges of the mass, the long tube-like perforations which have escaped general observation, and which in the more compact and better preserved specimens can scarcely be seen. Position and Locality.—Abundant in the Wenlock limestone of Wenlock, Shropshire; also in the Aymestry limestone near Aymestry, Herefordshire. 3rd Old. Zoantharia (Blainv.) = Zoophyta helianthoidea (Johnston) = A dinaria (Dana). Animal with simple tentacles, perforated at the tip, and either six (Antipathacea), twelve (Madreporacea), or a larger number (Madrephyllacea). The individuals are either simple or compound, and either fleshy and naked, or with a strong internal, supporting calcareous corallum. The body is in all cases distinctly radiated by vertical, double, membranous lamellae extending from the short central stomach to the outer wall; which lamellae becoming calcified at the base in those possessing a corallum, form the stellate cells therein; each cell of the corallum is continued in the living state into a perfect individual. In the extreme young state, most coral-cells have six lamellae, and this number remains through life in the 1st Tribe, Antipathacea: subsequently a second cycle of six shorter lamellae is developed, one between each pair of larger, and this number remains permanent in all the genera of the 2nd Tribe, Madreporacea. In the other groups additional lamellae are intercalated between these. Mr Dana notices that in those groups which are more than twelve-rayed, there are usually three smaller between each pair of larger lamellae, and the number is a multiple of four, if over twenty-four; below this, if more than six, the lamellae are usually alternate, and the number a multiple of six. The Zoopliytaria having eight equal tentacles, and rays to the cells, belong to a different system. The Order is divided into the following Tribes : 1st, Antipathacea, having six tentacles and a horny axis, of which we have no fossil examples; 2nd, Madreporacea; 3rd, Madrephyllacea. 2nd Tribe. MADREPORACEA. Corallum composite ; composed entirely of cellular, or porous, calcareous sclerenchyme’; cells small; each cell with six primary cellulose, lamella; in the young state, usually receiving six alternating or secondary lamella; when adult, total number never exceeding twelve ,• interlamellar structure composed of small, irregular, often rudi mentary vesicular plates, never forming diaphragms ; cells remaining unfilled at base by age ; no epitheca. This Tribe contains the families, I Madreporidce ; 2 Poritidw ; 3 Palccoporidw. To this tribe I provisionally refer the genus Palcvopora on account of the twelve radiating lamellae to the cells; a number so characteristic of the Madreporacea generally, with which it also agrees in the cellular texture intervening between the individual stars. The main difference between the Palceoporce and the true Madrepores