of a few Brachiopoda. 259 



visible, but not very well defined ; smaller valve as wide as long, 

 operculiforra, slightly convex and flattened ; surface smooth, in- 

 terrupted only by a tew concentric lines of growth. Structure 

 punctuated; hinge-line straight; valves articulating by means 

 of two teeth in the larger valve and corresponding sockets in the 

 smaller one. In the interior of the dental valve, beneath the 

 deltidium, three short lamellar processes are seen to occupy about 

 a fifth of the length of the shell, the central one being the 

 longest and most elevated ; the other two, appearing at the base 

 of the dental plates, converge gradually towards the central one; 

 a longitudinal rounded elevation extends also along the middle 

 of the valve. In the interior of the smaller one on either side of the 

 sockets a wide, thickened, raised, granulated margin (limbe) 

 surrounds the shell, which on reaching the middle of the front 

 directs itself longitudinally inwards under the form of a narrow, 

 acute, elevated crest, and not much longer than half the leugth 

 of the valve ; on either side of this ridge and the inner edge of 

 the margin are seen two other rounded ridges covered with large 

 granulations. Dimensions variable. Length 2, width 1^, depth 

 11 lines. 



Obs. In external shape this species reminds us of several cre- 

 taceous forms, such as Thecidea tetragona, Roemer, rugosa, D'Orb. 

 &c. ; yet it is quite distinct from any, by the more simple arrange- 

 ments in the interior of its smaller valve, where none of those 

 numerous sinuated ridges exist. 



The arrangement in the interior of the smaller valve of the form 

 under notice bears some resemblance to a few specimens of The- 

 cidea rusticajrom. the Lias of Ilminster, but of which unfortunately 

 only the smaller valve is known ; and from the inspection of more 

 than a hundred specimens found by Mr. Moore, none seem to 

 have attained above a third of the dimensions presented by the 

 French shell. There appears to be also a dissimilarity in the 

 shape of the central ridge, which in Thecidea Deslongchampsii is 

 narrow, and acute in its whole length in the specimens I have 

 been able to examine, while in Th. rustica it apparently forms a 

 double ridge united at the extremity, with an intermediate de- 

 pression. We have therefore ventured to distinguish the large 

 French Thecidea by the name of Th. Deslongchampsii, that gen- 

 tleman having first observed the species at May near Caen. 



Plate XIV. fig. 6. Natural size. Fig. 6 a, 7, 7 a, b, 8 & 9. Enlarged 

 illustrations. 



Thecidea Boichardii, Dav. PI. XIV. fig. 10, 11, 12. 



Thecidea Bouchardii, Dav. British Fossil Brachiopoda (Pal. Soc), 

 part 3. p. 14. pi. 1. fig. 15, 16 (1851). 



Diagnosis. Shell inequivalve, transversely oval, much wider 



