Mr. T. Davidson on French Liasic Spirifers. 265 



in the Liasic beds of Signy-le-Petit, and well described by that 

 author, but incorrectly figured by the artist; to which point 

 M. Buvignier called my attention by sending me the correct 

 illustrations here given, and a plaster-of-Paris cast both of this 

 and of his Sp. oxypterus, wherein the well-defined mesial fold 

 formed by a single plait, omitted in the original figures, is clearly 

 exposed, and which character fully distinguishes it from my Spi- 

 7'ifer Tessoni, as admitted by M. Buvignier, to whose opinion I 

 submitted my observations. 



Plate XV. fig. 3. From a drawing sent mB by M. Buvignier ; the specimen 

 was found in the Lias of the Ardennes. 



6. Spirifer Tessoni, Dav. 1852. PI. XV. fig. 1, 2. 



Diagnosis. Shell inequivalve, transversely oval ; valves convex, 

 ornamented by a variable number of small plaits, from forty to 

 sixty on each valve, more than half of which are formed by the 

 bifurcation and intercalation of plaits, at variable distances from 

 the beak and umbo ; the mesial fold is more or less produced, 

 gradually arising from the lateral portion of the valve, and orna- 

 mented by a variable number of plaits in width equalling those 

 ornamenting the rest of the surface; beak produced, nearly 

 straight ; area triangular ; deltidium in two pieces ; hinge-line 

 shorter than the width of the shell ; structure punctuated and 

 spinose ; numerous concentric lines of growth intersecting the 

 longitudinal radiating plaits ; dimensions variable. Length 22|^, 

 width 35, depth 16 lines. 



Obs. This magnificent Spirifer j by far the largest of the tribe 

 met with in the Lias of France, has been known to me these 

 several years, and was first discovered by M. Tesson and Des- 

 longchamps in the Liasic beds of Fontaine-etoupe-four, whence 

 not more than about half-a-dozen specimens had been procured 

 until lately, when M. Deslongchamps was so fortunate as to ob- 

 tain several from the Lias near May in the neighbourhood of 

 Caen, from which place the largest specimen was brought by that 

 learned and indefatigable palseontologist. This species has also 

 been encountered in the first-named locality by MM. Moriere and 

 Breville. It is at once distinguished from all the other Spirifers 

 by its dimensions and numerous small bifurcated plaits. 



Plate XV. fig. 1, From a perfect specimen found in the Lias of Fontaine- 

 etoupe-four near Caen, by M. Tesson. I am indebted to my 

 friend M. Bouet for the drawings of this shell. Fig. 2. The largest 

 specimen of this species yet discovered, and belonging to M. 

 Deslongchamps ; that gentleman prepared the drawing of this 

 shell, every plait of which he measured and most correctly repre- 

 sented. The specimen is also from May near Caen. 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. ix. 18 



