URASTER. 



101 



slab; among these are scattered smaller and more slender spines Avith traces of pedicellaria ; 

 the wide arabidacral valleys are bordered by two marginal rows of thin plates, which lie 

 obliquely on each other, with steep sides towards the valley, and having on their convex 

 under surface four or five elevations with concave summits, to which the moveable 

 marginal spines of the rays were articulated (fig. 1, h). 



The Avide ambulacral valleys are flattened, and of nearly the same breadth throughout, 

 they taper a little towards the mouth and the end of tlie ray (tig. I a) ; the narrow depression 

 down the centre indicates the suture by which the ambulacral ossicula were articulated along 

 the raesialline of the ray; these bones (fig. 1,^) "are narrow and linear in shape, slightly bent, 

 with the appearance of a very shallow sigmoid curve. This is caused by the curved keel 

 Avhich runs down each, grooved throughout two thirds of its length, but depressed and 

 marked with two pit-like impressions in the neighbourhood of the ambulacral sulcus (fig. 

 1, h) ; the ends of the ossicula which go to form the sulcus are slightly denticulated. The 

 curvation of the ossicula has reference to the disposition of the suckers, which in this genus 

 are arranged in four series down each avenue. The perforations are slightly ovate in this 

 species." Porbes, In figure 1, I have given an enlarged drawing of four of the ambulacral 

 ossicula, and the corresponding bordering plate, with its raammillary articulating surfaces 

 and spiny l^orders, for a comparison with the homologous parts of the ray in the living 

 Uraster rubens (fig. 3). 



Affinities and differetices. — The structure of the ambulacral skeleton, which is so 

 admirably preserved in this fossil, removes all doubt as to its true generic position and 

 affinities. It approaches so much, in fact, the existing Uraster rubens, Lin., of our coasts, 

 that it requires a careful comparison of its specific characters to determine the distinction 

 which undoubtedly exists between this Star- fish of the Lias sea and that of our own time. 

 It resembles in form Uraster carinatus, Wr., of the Marlstone of Yorkshire, but the promi- 

 nent dorsal ridges in that species appear to be absent in Uraster Gaveyi. 



Locality and Strati graphical position. — This beautiful specimen was discovered by 

 my friend, G. E. Gavey, Esq., E.G.S., in a slab of Middle Lias from Mickelton Tunnel, 

 near Chipping Campden, Gloucestershire, on the Oxford, Worcester, and Wolverhampton 

 Railway. The rock on which it lies belongs to the Zone of Ammonites capricornus ; with it 

 are associated the following species of Echinoderms : Cidaris Edwardsii, Wr. ; Hemipedina 

 Bowerbankii, Wr. ; Tropidaster pectinatus, Forb. ; Palceocoma Gaveyi, Wr. ; and 

 Pentacrinus robustus, Wr. 



Uraster carinatus, Wright, n. sp. PI. II, fig. 1. 



Rays five, long, and moderately lanceolate ; upper surface of the disc crowded with 

 short, thick spines ; upper surface of the rays provided with three prominent carinae, each 



