Mr. T. Davidson on French Liasic Spirifers. 261 



servable in the interior of the perforated valve; but all those 

 found in the Lias appear to belong to one group, presenting the 

 same internal dispositions of the septa in the larger valve and 

 spirals in the smaller one*; in all, the structure is punctuated 

 and spinose, and in different species varying only in the size of 

 the punctures and position and dimensions of the tubular spines. 

 To this group If. D'Orbigny has applied the generic appellation 

 of Spiriferina f, and it has also been clearly established, that Spi- 

 rifers possessing this structure were not only peculiar to the Lias, 

 as at one time supposed, but that they occur likewise in older 

 rocks. Liasic Spirifers appear to have been first noticed by 

 Knorr in 1755, and Torrubia in 1773; these authors having 

 illustrated Sp. rostratus, and Walcot in 1799 Spirifer Walcotti; 

 it was only however in the nineteenth century that these Spirifers 

 were properly named and described, but unfortunately too much 

 subdivided by various authors, who did not perceive that they 

 were making distinct species of mere varieties. 



Our researches have brought to light seven well-defined French 

 Liasic Spirifers, all described in this monograph. 



M. D'Orbigny, in his ' Prodrome,' gives a list of seven Liasic 

 Spirifers, three only of which are properly named; of the re- 

 maining four, three are synonyms of Sp. rostratus, so that 



* These have been fully described in my Monograph of British Oolite 

 and Liasic Brachiopoda, Part 3. p. 22, published by the Pal. Soc. 



t M. D'Orbigny divides the family of Spiriferidee into five genera, viz. — 

 1. Cyrthia; 2. Spirifer; 3. Spiriferina ; 4. Spirigerina ; b. Spirigera. 

 The three first only are in our view true Spirifers. In Cyrthia, M. D'Or- 

 bigny states the fissures to be covered by a deltidium ; in the second, Spi- 

 rifer, and third, Spiriferina, he mentions the fissure to be triangular, open 

 in all its extent, and without deltidium. We cannot here help expressing 

 our surprise at such an assertion from such an observer as M. D'Orbigny ; 

 we have no hesitation in stating our conviction to be, that in the perfect state 

 all Spirifers were provided with a deltidium, and only wanting from the in- 

 complete state of most specimens ; but we have often noticed it in many 

 species belonging to M. D'Orbigny's genera Spirifer and Spiriferina ; it is 

 not rare to find it preserved in many Liasic species from Normandy, and we 

 have figured it in our Monograph of British Liasic and Oolitic Brachio- 

 poda, it being composed of two pieces circumscribing a part of the orifice 

 through which the muscular fibres of the pedicle issued. M. Bouchard has 

 seen it preserved on some specimens of Sp. Verneuilii from Ferque, and I 

 figured a specimen of the same in Lamarck's collection (Ann. and Mag. 

 Nat. Hist. June InjO). It is beautifully preserved in many specimens of 

 Sp. speciosus from the Eifel. M. de Verneuil figured it in Spirifer Pellico : 

 in fact, in no case do I believe the triangular fissure was entirely open for 

 the passage of the muscular fibres. In one set of Spirifers, such as Sp. tra- 

 pezoidalis {Cyrthia), it covered all the fissure, but in others only a portion. 

 In Spiriferina M. D'Orbigny states the deltidial fissure to be edged by a 

 rim (bourrelet), which he gives as a distinctive character from Spirifer. 

 This is another mistake ; the rim alluded to exists in all Spirifers (see 

 Cours ele'mentaire de Palaeontologie, vol. ii. p. 86). 



