24 



ASTEROIDEA. 



transverse ossicles, the basal joints of which are greatly enlarged, thickened, and^ placed 

 in vertical pairs to form the mouth. 



Genus 8. T^ni aster, Billings. — Body deeply stellate ; no disc or marginal plates ; 

 rays long, slender, flexible, and covered with small spines ; two rows of large ambulacral 

 pores ; adambulacral plates elongated and sloping outwards so that they partly overlap each 

 other ; adambulacral ossicula contracted in the middle, dilated at each end. Generic name 

 from tcenia, a riband. 



PaltEaster. — Hall. 



Palceaster asperrimus, Salter (Annals and Mag. of Nat. Hist., 2d series, vol. 20, p. 325, 



pi. ix, fig. 1) fig. 15\ 



Fig. 15. 



Rays five, short, round and obtuse; upper surface con- 

 vex (1), and ornamented with many longitudinal rows of promi- 

 nent tubercles ; a single madreporiform body at the angle 

 between two rays. Ambulacra wide ; grooves deep, bordered 

 by two rows of large, transverse, marginal, adambulacral ossicula, 

 with acute ridges on their under side {\ a). 



Locality. — Collected by the Geological Survey in the Cara- 

 doc or Bala sandstones, near Welchpool, N. Wales. 



Palaaster obtusus, Forbes. Mem. Geol. Surv., Decade 1, pi. i, 

 fig. 3, 1849. 



"Body rather broad, convex above, spinosely reticulated; 

 spines very short, and probably grouped in tufts. The arms are 

 short, convex above, broad, oblong, and obtuse. Their under 

 surfaces exhibit oblong, rather broad, ambulacral plates, 

 gradually decreasing in size towards the tips of the arms, 

 but nearly equal for about two thirds of their length ; the am- 

 Fig. 1. Paiaaster asperrimus. Salt, bulacral sulcus betwceu them is rather broad. The largest speci- 

 men examined measured an inch and a half across." 



Fig. 2. Stenaster Salteri, Billings. 



Locality. — Pirst found in Lower Silurian rocks at Drumcannon, near Waterford, in 

 1846, by Sir Henry de la Beche, Captain James, R.E., and Professor Forbes, and by the 

 Geological Surveyors in the ash-bed of the Bala rocks. West of Bala Lake, North Wales. 

 In the Irish locality it was associated with Phacops Jamesii and numerous Orthides. In 

 the Welsh, with Trilobites of the genera Asaphus, and Homalonotus. Brachiopoda of the 

 genus Orthides, and numerous stems of Encrinites. 



