518 



FOSSILS OF THE MOUNTAIN LIMESTONE. [Ch. XXT. 



Fig. 571. Fig. 572. 



Spirifer trigonalds, Martin, sp. 

 Mountain Limestone. Derbyshire, &c. 



Spirifer glaber, Martin, sp. 

 Mountain Limestone. 



more numerously represented in these carboniferous rocks than in the 

 secondary formations described in former chapters; individually, as 

 Professor Ramsay has observed,* they may outnumber the lamellibran- 

 chiate mollusks, although the species of carboniferous lamellibranchiate 

 more than double the contemporary brachiopoda. The increasing num 

 ber of the last-mentioned group among the bivalve mollusca, both in 

 genera, species, and individuals, will be found to be a marked feature 

 in the fauna of the primary rocks the lower we descend in the series. 

 Among the brachiopoda or palliobranchiate mollusks, Terebratula 

 hastata deserves mention, not only for its wide range, but because it 

 often retains the pattern of the original colored stripes which orna- 

 mented the living shell. (See fig. 573.) These colored bands are also 

 preserved in several lamellibranchiate bivalves, as in Aviculopecten 

 (fig. 574), in which dark stripes alternate with a light ground. In some 

 also of the spiral univalves, the pattern of the original painting is dis 

 tinctly retained, as in Pleurotomaria (fig. 575), which displays wavy 

 blotches, resembling the coloring in many recent Trochidse. 



Fig. 573. 



Fiff. 574. 



Fig. 575. 



Terebratula hastata, Sow., 

 with radiating bands of 

 color. Mountain Lime- 

 stone. Derbyshire ; Ire- 

 land : Eussia, &c. 



Aviculopecten sublobaius, 

 Phill. Mountain Lime- 

 stone, Derbyshire ; 

 Yorkshire. 



Pleurotomaria carinata, Sow. 



(P. flammigera, Phill.) 

 Mo untain Limestone. Derby- 

 shire, &c. 



The mere fact that shells of such high antiquity should have pre- 

 served the patterns of their coloring is striking and unexpected ; but 

 Professor E. Forbes has deduced from it an important geological con- 

 clusion. He infers that the depth of the primeval seas in which the 

 Mountain Limestone was formed did not exceed fifty fathoms. To 



* Geol. Quart. Journ., p. 41, 1864. 



