262 Mr. T. Davidson on French Liasic Spirifers. 



M. D'Orbigny seems only acquainted with five; we have added 

 two others which are by no means the least interesting of the lot, 

 viz. Sp. Tessoni and Sp. Deslongchampsii, Sp. Tessoni and ros- 

 tratus being the two largest of the tribe peculiar to the Lias. In 

 Great Britain we are acquainted with only three of these French 

 species, viz. Sp. rostratus, Walcotti and Munsteri ; but another 

 is there found, described by us under the name of Sp. Ilmin- 

 steriensis. Sp. Linguiferoides and Chilensis, Forbes, as well as 

 Sp. tumidus (Coquand and Bayle), Sp. Hartmanni and verrucosus, 

 Zieten, as we have stated, seem to us only varieties of Sp. ros- 

 tratus ; and Sp. Beirensis (Sharpe) is probably also another vari- 

 ation of the same. We are therefore acquainted with only eight 

 or nine species of Spirifer from the Liasic period, seven of which 

 are found in France, some bearing much external resemblance 

 to certain Palaeozoic forms. 



Spirifers were most abundant in species in the Silurian, Devo- 

 nian, and Carboniferous periods, less so in the Permian and 

 Lias, and not positively known to occur higher up in the series, 

 although I should not be surprised if they were found higher up. 

 The limits assigned to certain genera are often contradicted by 

 unexpected discoveries : within the last few years Producta have 

 been shown to occur in the Silurian rocks, Leptcena, Thecidete 

 in the Lias, and other genera have likewise been made to descend 

 or to rise in the series. 



1. Spirifer rostratus, Sch. sp. 1813. PI. XIV. fig. 14, 15. 

 Pl.XV.fig.il. 



Terebratulites rostratus, Schlotheim, Beitrage zur Nat. p. 73, 

 1813, and Nach. zur Petrefact. pi. 16, 1822. 



Diagnosis. Shell inequivalve, variable in shape, transversely 

 oval or elongated, with or without a mesial fold and sinus, 

 smooth or ornamented by numerous small shallow rounded 

 costse, never extending over the mesial fold or sinus ; beak more 

 or less developed, recurved or straight ; deltidium in two pieces ; 

 area well-defined, variable in dimensions, but whose limits are 

 marked by the absence of spines ; hinge-line shorter than the 

 width of the shell ; structure punctuated and spinose ; spines 

 irregularly disposed over its surface ; dimensions variable. Length 

 19, width 22, depth 12 lines. 



Obs. This species is so well known that we need not enter into 

 any lengthened details, but merely remark that much larger spe- 

 cimens have been collected in England than in France ; one in 

 particular, discovered at Ilminster by Mr. Moore, measured, 

 length 28, width 30, depth 17 lines. S. rostratus is found in 

 many countries, but especially abundant in the Liasic quarries in 



