LUIDIA. 



Ill 



A. — Sjjecies from the Lias. 

 LuiDiA MuRCHisoNi, WiUiamson. PI. V, fig. 2. 



LuiDiA MuRcnisoNi, Williamson. Magazine of Nat. History, vol. ix, p. 425, 1836. 



- — MuKCHisoNi, Forbes. Mem. of the Geol. Surv., vol. ii, part 2, p. 480. 

 LuiDiA MuKCiiisoNi, Forbes, in Morris's Catalogue of British Fossils, 2d ed., p. 83. 

 SoLASTEK POLYNEMiA, Simpson. Fossils of the Yorkshire Lias, p. 135, 1855. 

 LuiDiA MuKCHisoNi, Wright. British Association Report, vol. for 1S56, p. 402. 



Rays twenty, moderate in length, obtuse at the apex, and having their margins fringed 

 with numerous short, hair-hke spines, mouth opening large, with impressions of radial 

 processes. 



Description. — This unique fossil Star-fish is so imperfectly preserved that only a few 

 of its characters can be ascertained. It was first figured and described by Professor 

 Williamson, in the ninth volume of Loudon's ' Magazine of Natm^al History' for 183fi, and 

 was thus described : 



" This fossil was found in the marlstone at the point Avhere it is carried up into the 

 cliff to the north of the great fault, at the Peak Hill near Robin Hood's Bay, near the 

 lower part of the stratum, where it blends with the lower lias. The slab on which the 

 fossil is preserved is of a rather micaceous nature, a matrix, generally unfavorable for pre- 

 serving minute characters ; and a portion of the fossil having adhered to the upper part 

 of the rock which fell in pieces, the view presented is rather that of the internal than the 

 external structure of the animal. The central circle, the situation of the mouth, is pre- 

 served very distinctly, and proceeding with considerable regularity from this, is a series of 

 rays, twenty in number. Those rays near their base bear the sulcus (furrow) which runs 

 under those of recent Asteria; ; but towards their apex they become more worn and thin, 

 showing in several places a small wiry line, with short ribs branching ofl" at right angles, 

 apparently a species of appendage, resembling what represents the vertebral column and 

 ribs in the turtle^ and which is observable in recent Asterige. There are also slight traces of 

 transverse grooves on the whole surface of each ray ; but these are generally almost 

 obliterated. Along the margins are extremely regular rows of small rhomboidal perforations, 

 or cells, from which proceed a series of lateral filaments, or delicate lengthened papillae ; 

 but on the surface of the fossil, it merely presenting to us the interior, no papillae are pre- 

 served. The apex of such rays as have not been broken off prior to the animal being 

 entombed, are obtusely pointed." 



Locality and Stratigrapldcal position. — From the appearance of the shale in which this 

 specimen is embedded, it appears to come from the zone of Ammonites capricornus, 

 it therefore belongs to the Middle Lias, and occupies about the same horizon as Uraster 

 Gaveyi, Wr., from the Middle Lias of Gloucestershire. 



