THE UPPER SILURIAN PERIOD. 



12 



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 (Limult) of exist- 

 ing seas also appear to have been 

 represented by at least one form 

 (Neolimulus) in the Upper Silu- 

 rian. 



Coming to the Mottusca, 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 Glaticonome, and species of 

 Ptilodiclya (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 Orlhis, Strophomena, and Leptana 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 Spirifcra and Pentamenis. 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. Pterygotut Anglicus, 

 viewed from the under side, reduced 

 in size, and restored, c c, The feelers 

 (antennae), terminating in nipping- 

 claws ; o o, Eyes ; in in, Three pairs of 

 jointed limbs, with pointed extremi- 

 ties ; n n, Swimming-paddles, the bases 

 of which are spiny and act as jaws. 

 Upper Silurian, Lanarkshire. (After 

 Henry Woodward.) 



