346 BRACHIOPODA OF THE 



Orthis Monnieri, de Tromelin et Lebesconte. Bull. Soc. Geol. de France, 3rd ser., 



vol. iv, p. 595, 1876. 



Shell circular, or more often elongated, oval, slightly widest anteriorly; hinge-line 

 straight, about half the breadth of the shell. Ventral valve moderately convex ; beak 

 slightly incurved ; area narrow and small, divided in the middle by a rather wide fissure. 

 Dorsal valve less convex than the ventral one, slightly depressed along the middle. 

 Surface of both valves marked by numerous fine, radiating, thread-like striae, which 

 increase in number by the interpolation of shorter and smaller ones. In the interior of 

 the ventral valve two large, deep, oval, muscular depressions occupy fully two-thirds of 

 the length of the valve, and are divided in the middle by a narrow, angular, slightly 

 projecting ridge. In the interior of the dorsal valve a small bilobed cardinal process 

 is situated between the prominent, diverging, slightly curved, brachial processes ; with a 

 convex rounded ridge, extending from under the cardinal process to about half the length 

 of the valve ; on either side are situated rather large, elongated, adductor muscular 

 impressions. Two specimens measured — 

 Length 7, width 7 lines. 

 5 4 



Obs. — In 1869 I described this species by the name of Orthis Vicaryi, but since then 

 M. de Tromelin has assured me that the shell so named was the same as the one named 

 Orthis Monnieri by M. Rouault. It was, however, impossible for me or any one else 

 to make out the shape and character of the shell from Rouault's so-termed description. 

 He says : " Cette espece, par le rapprochement tres marque des deux divisions qui 

 naissent de l'impression interne du crochet de la valve dorsale [our ventral] et qui s'etendent 

 sur la partie mediane de la coquille, se montre en general assez differente des exemplaires 

 de l'espece qui se trouve dans le Gres de May, et que l'on croit devoir rapporter a Orthis 

 redux, Barr., et qui nous parait plutot devoir se rapprocher de celle de Gahard. Celle-ci, 

 a cause de son abondance, nous a permis de reconnaitre que ses caracteres, d'abord differents 

 se modifient, et nous possedons maintenant, provenant du Gres Coquillier de Gahard, tout 

 les intermediaires necessaires pour justifier ce rapprochement que nous faisons entre les 

 echantillons de ces deux localites." 



I am quite ready to relinquish the name I gave to the fossil, although I can hardly 

 admit that the fossil had been previously described, nor was any figure given of it by M. 

 Rouault. I have, however, thanks to M. Lebesconte, been able to examine a number of 

 good examples of the French fossil, and they agree in every particular with our Budleigh- 

 Salterton specimens. 



MM. de Tromelin and Lebesconte quote it likewise from the Devonian of the 

 Cotentin and Rade de Brest. The same geologists state that the sandstone with 

 0. Monnieri constitutes an excellent horizon by which to determine the lower part of 

 the Devonian system in the Departement of the Manche, the Sarthe, Ille-et-Vilaine, 



