Ch. XXVI.] 



MIDDLE DEVONIAN. 



423 



With the above are found many stone-lilies or crinoids, some of them, 

 such as Cupressocrinites, of forms generically distinct from those of the 

 Carboniferous Limestone. The mollusks also are no less characteristic, 

 among which the genus Stringocephalus (fig. 558) may be mentioned as 



Fig. 558. 



Stringocephalus Burtini,Defr. (Terebratula porrecta, Sow.) Eifel; also South Devon. 



a. Valves united. b. Side view of same, 



c. Interior of larger valve, showing thick partition, and part of a large process which 

 projects from its upper end quite across the shell. 



exclusively Devonian. Many other Brachiopod shells, of the genus Spir- 

 ifer, &c, abounded, and among them the Atrypa reticularis, Linn. sp. 

 (fig. 575, p. 434), which seems to have been a cosmopolite species oc- 

 curring in Devonian strata from America to Asia Minor, and which, as 

 we shall hereafter see (p. 433), lived also in the Silurian seas. Among 

 the peculiar lamellibranchiate bivalves common to the Plymouth lime- 

 stone of Devonshire and the Continent, we find the Megalodon (fig. 559), 

 together with many spiral univalves, such as Murchisonia, Euomphalus, 

 and Macrocheilus ; and Pteropods such as Conularia (fig. 560). The 



Fig. 560. 



Fig. 559. 



Megalodon cucullatus, Sow. Eifel ; also Bradley, S. Devon. Conularia ornata, D'Arch. et 



a. The valves united. Dc Vern> 



6. Interior of valve, showing the large cardinal tooth. (Geol. Trans. 2d s. vol. vi. pi. 29.) 



Eefrath, near Cologne. 



cephalopoda, such as Cyrtoceras, Gyroceras, and others, are nearly all of 

 genera distinct from those prevailing in the Upper Devonian Limestone, 

 or Clymenien-kalk of the Germans already mentioned (p. 421). Although 

 but few species of Trilobites occur, the characteristic Brontes flabellifer 

 (fig. 561 p. 424) is far more rare, and all collectors are familiar with its 

 fan-like tail. The head is seldom found perfect ; a restoration of it has 

 been attempted by Mr. Salter (fig. 562). 



In this same formation, comprising in it the " Stringocephalus Lime- 



