THE UPPER SILURIAN PERIOD. 



125 



narrow, sword-shaped spine. Fragments of the skeleton are 

 easily recognised by the peculiar scale-like markings with 

 which the surface is adorned, and 

 which look not at all unlike the 

 scales of a fish. The most fam- 

 ous locality for these great Crus- 

 taceans is Lesmahagow, in Lan- 

 arkshire, where many different 

 species have been found. The 

 true King-crabs (Liinuli) of exist- 

 ing seas also appear to have been 

 represented by at least one form 

 {Neolimulus) in the Upper Silu- 

 rian. 



Coining to the Mollusca, we 

 note the occurrence of the same 

 great groups as in the Lower 

 Silurian. Amongst the Sea- 

 mosses {Polyzod), we have the 

 ancient Lace - corals (Fenestella 

 and Retepora), with the nearly- 

 allied Gfawonome, and species of 

 Ptilodictya (fig. 66) ; whilst many 

 forms often referred here may 

 probably have to be transferred 

 to the Corals, just as some so- 

 called Corals will ultimately be 

 removed to the present group. 



The Brachiopods continued 

 to flourish during the Upper 

 Silurian period in immense num- 

 bers and under a greatly in- 

 creased variety of forms. The three prominent Lower 

 Silurian genera Orihis, Strophomena, and Lepttzna are still 

 well represented, though they have lost their former pre- 

 eminence. Amongst the numerous types which have now 

 come upon the scene for the first time, or which have now a 

 special development, are Spirifera and Pentamerus. In the 

 first of these (fig. 69, b, c), one of the valves of the shell (the 

 dorsal) is furnished in its interior with a pair of great calca- 

 reous spires, which served for the support of the long and 

 fringed fleshy processes or " arms " which were attached to the 

 sides of the mouth.* In the genus Pentamerus (fig. 70) the 



* In all the Lamp-shells the mouth is provided with two long fleshy 

 organs, which carry delicate filaments on their sides, and which are 

 10 



Fig. 65. Pttrygot* 

 ewed from the under 

 n size, and restored, c < 

 antennae), terminating 

 ~aws ; o o, Eyes ; m in, Three pairs of 

 ointed limbs, with pointed extremi- 

 ics ; it 11, Swimming-paddles, the bases 



of which are spiny and act as jaws. 



Upper Silurian, Lanarkshire. (After 



Henry Woodward.) 



