STRATIGRAPHIOAL DISTRIBUTION. 



35 



Pal.eodiscus. — Salter. 



This genus has been proposed by Mr. Salter for a unique Asteroid, found at 

 Leintwardine. The disc, which is incomplete, is formed of large, irregular, rhomboidal plates, 

 whicli radiate in seven or eight rows from the mouth in each inter-ambulacral space, and 

 are furnished with short spines. The only specimen at present known is 



Palceodiscus ferox, Salt. "Ann. and Mag. Nat. Mist.,' 2d series, vol. xx, p. 333, PI. 



IX, fig. 6. 



"The inner angles of the inter-ambulacra (fig. 18) form a prominent triangular boss, 

 cut off distinctly by a furrow, and between these are the 

 large elongated basal plates of the ambulacra, lying parallel, 

 and not at all divergent ; they are thick and blunt, and 

 together with the five bosses form a circumscribed star in 

 the centre, the massive character of which contrasts strik- 

 ingly with the thinness and delicacy of all the other parts 

 either of the ambulacra or disc. The ambulacra are 

 small, composed of a double row of transverse plates, 

 narrow, and more crowded than in Palasterina or 

 Palaaster, and apparently very thin in texture. They 

 can be detached and leave the upper plated surface free, which is covered with irregular 

 plates. If there be no deception in this — for we have only a single specimen— the 

 aflnnity would be much closer with the forms abov(i mentioned, although the strong 

 oral apparatus reminds us more nearly of Protasfer. 



JLocality. — Leintwardine, in Lower LudloAV Rock ; t he only specimen is in the cabinet of 

 Mr. Marston, of Ludlow. 



Professor Porbes^ described under the name Lejiida-^ter Grai/l a remarkable Echinoderm 

 from the Wenlock limestone of Castle Hill, Dudley, which at first glance bears a resemblance 

 to Solaster, a closer examination of its structure, however, shows that it possesses 

 characters which justify its separation into a distinct genus, so widely different from 

 other Asteriadce, that it may possibly form a connecting link between that order and the 

 CrinoideiB . 



''The disc of Lepidaster,'' says Professor Porbes, "is very little more than two inches 

 in diameter. It is, unfortunately, so much injured, that the elements cannot be clearly made 



' 'Memoirs of the Geological Survey,' decade iii. 



Fig. 18. 



Palaodlscui ferox, Salt. 



