266 Mr. T. Davidson on French Liasic Spirifers. 



7. Spirifer Deslongchampsii, Dav. PI. XV. fig. 4. 



Unfortunately only the smaller valve of this curious species 

 has been collected as yet by M. Bouchard, in the Lias of Fon- 

 taine-etoupe-four ; its description must consequently be very in- 

 complete ; but it seems to differ from all the other forms we have 

 examined by its shape and structure. 



Diagnosis. Shell inequivalve, transverse, ornamented by fifteen 

 or sixteen costse, several of which arise from bifurcation and in- 

 tercalation at variable distances from the umbo ; no real mesial 

 fold ; four or five of the costse slightly projecting above the level 

 of the lateral ones ; structure punctuated and spinose. Length 7, 

 width 10 lines. 



Obs. The structure of this shell is very beautifully exposed on 

 the specimen under notice ; it is closely and largely punctuated 

 all over, but it is only on the upper surface of the rounded costse 

 that the tubular spines are implanted, few in number, and very 

 wide in circumference at their base ; none appear on the sides or 

 the grooves left between the plaits, as in other Liasic Spirifers. 

 The spines are broken, unfortunately, near their base, but are so 

 distinct and so few in number that they can easily be counted 

 without the use of the lens. This remarkable shell was kindly 

 forwarded to me by my friend M. Bouchard for description and 

 illustration. 



Plate XV. fig. 4. The line represents the real width of the specimen. 

 Fig. 4 a. The valve enlarged 4 times. Fig. 4 b. A fragment con- 

 siderably magnified ; one of the spines is restored. 



EXPLANATION OF THE PLATES AND FIGURES. 



Plate XIII. 



Fig. 1. 1 a, b. Rhynchonella psittacea (recent) : 1. interior of small valve ; 

 1 a. interior of large valve ; 1 b. section of small valve. 



— 2. Rhynchonella octoplicata, Sow. ; interior of small valve. 



— 3. Do. do. ; beak, foramen, and deltidium (which is 



tubular in this species). 



— 4. Do. Bo ueti, Dav. ; interior of perforated valve. 



— 5. 5 a. Do. do. ; exterior. 



— 6. Do. concinna, Sow. ; beak and foramen, which is not en- 



tirely surrounded by the deltidium. 



— 7- Do. tetrahedra, Sow. ; beak, which is so much recurved as 



to show no foramen or deltidium. 



— 8. Do. sub-Wilsoni, D'Orb. ; interior of smaller valve en- 



larged. 



— 9. Do. do. ; interior of larger valve, enlarged. 



— 10. Do. do. ; a specimen, nat. size, of larger valve. 



— 10 a. Do do. ; a gutta percha cast made from fig. 10, 



to show the difference presented in similar casts of T. Wiisoni, 

 fig. 14 B. 



