SPIRIFER. 21 



Delthyris Hartmanii, Quenstedt. 1843. Das Floegibirge, Wurtemberg, p. 181. 



— verrucosa, Quenstedt. 1843. Das Floegibirge, Wurtemberg, p. 185. 



— rostrata, Quenstedt. 1843. Das Floegibirge, Wurtemberg, p. 186. 

 Spirifer punctatus, Buckman. 1845. Geol. of Chelt., pi. 10, fig. 7. 



— reticulatus, Buckman. (MS.) 



— linguiferoides and Chiliensis, Forbes and Darwin. 1846. South 



America, p. 267, pi. 5, figs. 15, 16, 17, 18. 



— rostratus, Dav. 1847. London Geol. Journal, vol. i, p. 109, pi. 18, 



figs. 1—10. 

 Spiriferina granulosa, Roemer (according to M. D' ' Orbigny) . 1849. Prodrome, p. 56. 



— verrucosa, D'Orb. 1849. Prodrome, vol. i, p. 221. 



— Hartmanii, D'Orb. 1849. Prodrome, vol. i, p. 2^9. 

 Spirifer rostratus, Bronn. 1849. Index Palseont., p. 1181. 



— tumidus, Coquand et Bayle. 1850. Bull. Soc. Geol. de France, vol. vii, 

 2 de Serie, p. 235. 



Diagnosis. Shell iniquivalved, variable, rounded, with mesial fold and sinus more or 

 less prominent ; surface smooth or undulated, forming sometimes rounded plaits ; beak 

 more or less developed, recurved or straight ; deltidium in two pieces, area well defined, 

 surface of valves punctuated, and spinose extending only to the edge of the area. Three 

 lamellae are seen in the interior of large valve, the central one more elevated, and termi- 

 nating in a point ; in small valve, two spirals united together by a lamella. Length and 

 depth very variable, the largest specimen known measuring — length 28, width 30, depth 

 17 lines; but the dimensions are generally much smaller, rarely extending 10 lines in 

 length, and the same in breadth. 



Obs. The numerous variations in size and form assumed by this species, does not admit 

 of a correct description ; but, through a numerous suite of specimens, we are enabled to 

 trace the passages from one variation of form into another, all preserving a general aspect, 

 leading to the most common type. Since 1845, I have devoted much attention to this 

 species, having had at my disposal a great number of specimens from our British and 

 foreign localities, it being abundantly spread in different beds of the liasic period, and a 

 few of the most marked variations are illustrated in Plate II; and, had space admitted of 

 it, the intermediate passages could have been traced. All the figures, excepting 18 and 19, 

 are of the natural size ; fig. 1 represents the largest specimen yet known of the species, 

 which varies in size from the one first mentioned to that of a pea. The average dimensions 

 and shapes are illustrated by figures 1, 2, 5, and 7. 



The great variations to which this species is subject appear attributable to three principal 

 causes -. — First. The presence of a mesial fold and sinus more or less developed, or its total 

 absence, as seen in some specimens where the front is quite straight (figs. 4 and 10) ; at 

 other times only a gently elevated curve is perceptible, as in fig. 11. The large valve being 

 regularly convex to the front, and no sinus existing, as generally happens when there is a 

 mesial fold, more or less produced, as in figs. 1, 2, and 7. The second cause exists in 

 the tendency there is in certain specimens to undulation, which, becoming close, often 



