82 INTRODUCTION. 



I cannot conclude these few remarks without mentioning how much science is in- 

 debted to the late Baron von Buch/ M. de Koninck,^ De Verneuil/ Prof. M'Coy, and 

 others, for their numerous investigations of the species composing this extensive genus. 



Geol. range. — True Spirifers first made their appearance in the lower Silurian epoch, 

 and continued to exist all through the Palseozoic formations, the last well authenticated 

 examples being found in the Trias ? 



Examples .- Sp, Striatus, Martin, sp. ; Cyrtcena, Dal. ; Anossofi, Vern. ; Verneuili, 

 ArcJdaci, and Bouchardi, Murch. ; Mosquensis, Fischer, sp. ; Pailleti, Rojasi and Pellico, 

 de Verneuil; alatus, Schl. ; glaher, Sow.; &c. &c. 



Sub-section ^.— Spiriferina, B' Orhigny, 1847. 



Type — S. ROSTRATA, Schl., sp. Int., PL VI, fig. GO. 



Spirifer (part) of the generality of Authors. 

 Spiriferina, IfOrh., M'Coy, &c. 



Shell generally transverse ; valves unequally convex, with or without a mesial fold ; 

 surface smooth or costated ; beak straight or recurved ; area commonly largely developed 

 and interrupted by a pseudo-deltidiura, notched in the vicinity of the cardinal edge ; 

 shell structure punctated ; surface spinose ; hinge line commonly shorter than the width 

 of the shell ; valves articulating by means of a strong cardinal tooth situated on each side 

 at the base of the fissure, supported by strong largely developed vertical shelly plates, and 

 corresponding with sockets in the interior of the smaller valve ; the space intervening 

 between the dental plates in the interior of the ventral valve is occupied by the cardinal 

 muscles, which are divided by an elevated mesial septum, wide and thick at its base, but 

 gradually tapering into the shape of an acute blade, to the sides of which the adductor 

 was, no doubt, fixed ; in the interior of the dorsal valve the shelly lamellae destined to 

 support the cirrated arms assume the form of two large spiral horizontal cones,* 



Obs. Besides the important difference in shell structure, a largely developed mesial 

 septum exists in the punctated species, but no such plate is known to occur in the impunc- 

 tate forms. It may, perhaps, therefore be preferable to follow M. d'Orbigny in adopting 

 Spiriferina as a sub-section of Spirifer, a view already embraced by Professor M'Coy.^ 



I "Uber Delthyris, 1837; and M^m. Soc. Geol. de France, vol. iv, 2d part, 1840. 



' Desc. des An. Foss. de la Belgique, 1842-44. 



^ Geol. of Russia and the Ural Mountains, vol. ii, 1845, &c. 



^ Some of the species belonging to this sub-section have been fully described in Part iii, under the 

 genus Spirifer. 



'" It is possible, that the Sp. heteroclyta, Def., Demarlii, Bouch., Hispanica, D'Orb. sp., and some 

 other Palaeozoic species, which are closely punctated, should be admitted into this sub-genus in preference 

 to Cyrtia, which is impunctate. 



