Abstract

T he genus Goniaster was proposed by Prof. Agassiz, in his ‘Prodrome,’ to include Starfishes with a large pentagonal body, having the margin bordered by a series of wide, thick plates or tesseræ, superimposed in pairs, and which support spines, granules, &c. The upper and under surface of the disk is covered with small polygonal plates, set closely together like a mosaic, and fitted into this marginal framework: the free surface of the ossicles is smooth or covered with granulations. The ambulacral furrows are narrow, with two rows of pedal suckers therein; the vent opens near the dorsal surface, and the mouth-opening is slit-like and pentagonal. Müller and Troschel, in their ‘System der Asteriden,’ suppressed the genus Goniaster , and instead thereof erected the genera Astrogonium , Goniodiscus , and Stellaster . The diagnostic characters of these groups were chiefly obtained from the structure of the marginal plates and appendages thereof, the figure and arrangement of the discal plates; and the form and development of the rays:— 1. Astrogonium . Marginal plates large and smooth towards the centre, their inner border encircled by granules. 2. Goniodiscus . Marginal plates having the entire upper surface covered with close-set granulations. 3. Stellaster . Marginal plates granulated, the ventral segment supporting a pendent spine, the rays elongated and tapering to a lanceolate extremity. Many of these characters are absent in fossil Goniasteridæ and are therefore valueless for palæontological purposes; for this reason I have retained the genus Goniaster for the large pentagonal short- rayed forms, and that of Stellaster for those with a smaller.

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