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Eciiinodermata.] LOWER PALAEOZOIC RADIATA. 59 ‘ madreporiform tubercle,’ marking the posterior side and forming the external termination of a peculiar organ termed the '■sand canal' extending from thence to the arterial circle round the mouth. The genital openings pierce the bony circle round the mouth. The mouth has no teeth; the oesophagus is short, and two large caeca extend into each ray, exposing the chyle to the veins, which latter communicate with a large circular venous trunk surrounding the mouth, and communicating by a vertical muscular tube, or heart, with a smaller arterial circle also surrounding the mouth and giving out branches to the mouth, to the intestine, others running between the ambulacra supplying the suckers, and perforating the in tegument at the tips of the ambulacra to supply the external membranes. The nervous system is distinct, one cord runs round the mouth, giving off three branches to each ray, one running between the ambulacra to the tip, where, according to Ehrenberg, it dilates to form a bulb or optic nerve, to supply a bright red point at the end of each ray, usually considered to be, in consequence, a true eye; the other two nervous branches supplying the viscera. The sexes of all the Starfishes are in distinct individuals, the ovaries in the one case, and testes in the other, forming bunches of slender cseca round the oesophagus, two at the origin of each ray. The following notice of the Palaeozoic Starfishes has been contributed by Prof. E. Forbes. As the specimens belonging to the University Collection have been figured by the Geological Survey, it has not been thought necessary to refigure them. Before I was aware Professor Forbes had described them it seemed to me that the U. Ruthveni and U. Ilirudo, as well as the similar American species, might be easily separated from the great star-fishes forming the recent genus Uraster, by their small size and much more simple skeletons, and I had named the genus Urasterella in my MSS. The U. Primcems I thought generically distinct from the other two, as the rays were not contracted at base &c.; and I had named it Palasterina, from its resemblance to the recent genus Asterina. “ True starfishes have rarely been met with in the older rocks. When they do occur, however, they are not likely to be overlooked, as their forms and structure cannot easily be confounded with those of the other radiata. At the same time, the fragility of the existing species and the difficulty attending their preservation entire, after death, reduce the chances of our finding them frequently in the fossil state. Such as do occur in Palseozoic rocks have a singular resemblance to existing forms, especially to those species which are characteristic of Northern seas. Hence it is convenient to retain them in known genera; for although parts may have been lost, and textures disappeared, which might have warranted their generic separation, there is nothing remaining to us of their organization which would not be consistent with that of existing Asteriadw of the generic groups to which they are here referred. Genus. URASTER (Agassiz). Uraster Rutitveni* (Fori.) Ref.— Forb. Mem. Geol. Surv. Dec. 1. t. 1. f. 1. “ Sp. Gh.—Disk small; arms rounded, very long, linear-lanceolate, subcarinate. Upper surface reticulated; interspaces irregular; under surface marked with the impressions of the double series of linear ambulacral ossiculse, each of which is slightly curved. “ The back and upper surface of arms of this species were probably covered with close set fasciculi of small ohtuse spines. Disk to ray as 1—5. Breadth of ray 0|. Breadth of Disk ^ inch. Length of ray IA. Uraster? hirudo (Forb.) Ref.—Forb. Mem. Geol. Surv. Dec. 1. t. 1. f. 4. “ £'p. Ch.—Disk very small; arms tapering, linear lanceolate, acuminate, contracted at their bases. Upper surface with radiating series of reticulated spinous bundles, placed very regularly, so that each ray appears * Named in compliment to the zeal and intelligence of Mr. John Ruthven, of Kendal, who has collected the greater part of the Westmoreland fossils—and is well acquainted with the structure of his native county. i 2