154 The Life-HiMonj of Spirifcr keci-s. 



the same cliaracters and peculiarities : the shape and its varia- 

 tions ; — the hinge-line, as to relative length compared Avith that 

 of the shell ; — the area and the aperture with its extent and 

 Yariation ; the swollen nature of the valves and the greater 

 prominence of the ventral valve ; — the prominent median fold 

 and the rounded nature of the side-plications, varying in' num- 

 ber, but always few, and often being obsolete near the side-mar- 

 gin and on the beak. The surface markings, too, i. e. the 

 radiating and concentric striffi, are characteristic, — the former 

 being tlie prints or bases of systems of spines, only seen by the 

 microscope. The size also agrees Avith that of the representa- 

 tives in the Niagara rocks of America. 



Before considering S. curvatus and related species, let us 

 notice the two species provisionally put by Davidson in D'Or- 

 bigny's subgenus Spirif&riiia. 



Spiriferina cristata, Schlotheim (sp.) var. (Biit. Dev. Bracli., 

 p. 46, PI. VI, Figs. 11 — 15, also Brit. Perm. Brach., p. IT, and 

 Carb. Monogr., pp. 38 and 226). Davidson expresses himself 

 as not able clearly to distinguish this species from either Sna. 

 cristata of the Carboniferous and Permian or Spirifer crispus 

 of the Silurian ; and he says — "The question of the origin and 

 recurrence of the Spiriferina avc are at present describing" 

 {Sna. cristata, Devonian, 1. c, p. 47), "is one of some diffi- 

 culty, demanding considerable attention and further research. 

 It is an exceedingly variable shell, being small (adult) in some 

 localities or strata, while in othei's it has attained considerably 

 larger dimensions" (at Lowe and CornAvall large, and at Darting- 

 ton small). "It is my strong impression that we must look for 

 its first appearance or orig'u in the Silurian time, and that it 

 , continued to be represented, with some slight modifications, in 

 the Devonian, Carboniferous, Permian, and perhai)S up to the 

 Jurassic period" (1. c, p. 47). 



Davidson identifies the Scottish Carboniferous Sim. cristata 

 and Sna. octoplicata with this species, and these with Schnur's 

 species Spirifer aculeatus. The species Spiriferina insculj)ta, 

 Phillips (sp.) var. (PI. VI, P'^igs. 16 and 17, 1. c, p. 48), appears 

 to be also closely related to these species. 



In the Silurian monograph, we find the variety Avith angular 

 plications, and more of them, called ;S'. sulcatus, Avhile S. crispus 



