RHYNCHONELLA. 83 



surrounded by the deltidial plates projecting in a tubular shape round the perforation ; 

 beak ridges not very distinct, the false area between them and the hinge margin being 

 small, and not much indenting the smaller valve ; valves smooth in the young shell, and 

 ornamented at a more advanced period by only a few rounded plaits appearing towards 

 the margin, viz., two or three, rarely more, forming a kind of mesial fold, to which 

 one or two plaits in the sinus of the larger valve correspond; likewise the sinus only 

 appears near the margin or in the anterior portion of the shell; on either side on both 

 valves, three or four similarly disposed costae are also visible; concentric lines of growth 

 distinctly marked. Structure unpunctuated ; length 7, width 7^, depth 5 lines. 



Obs. This little species was discovered in the Upper Lias of Ilminster, where it is 

 common, by Mr. Moore ; it has likewise been met with in beds of the same age, by Mr. H. 

 Miller, at Cromarty, in Scotland, and is quite distinct from all the species of Rhynchonella, 

 yet discovered in the Oolitic Period, and cannot be mistaken for R. variabilis, with 

 which it differs completely ; in some rare instances, instead of two or three plaits on the 

 mesial fold, I have found four and even five ; but this kind of variation is common to all 

 Rhynchonellse, and therefore cannot be taken into consideration. It gives me great pleasure 

 to name it after my valued friend, M. Bouchard. 



Figs. 3 and 4, represent two examples from the Upper Lias of Ilminster, in the 

 collection of Mr. Moore. 



Fig. 5. A specimen from Cromarty, in the collection of Mr. Miller. 



77. Rhynchonella varians, Schloth., Sp. Plate XVII, figs. 15, 16. 



Terebratulites varians, Schlotheim. 1820. Die Petrefactenkunde, p. 267; Ency. 



Meth., pi. 241, fig. 5"\ 



— obtrita. Befrance. 1828. Die. d'Hist. Nat., vol. liii, p. 161 ; Ency. 



Meth., pi. 241, fig. 5. 



— varians, Reenter. 1835. Die Vers, des Nord. Oolithen gebirges, 



tab. ii, fig. 12. 



— soctalis, Phillips. 1835. Illust. of the Geol. of York., part i, p. 135, 



pi. vi, fig. 8. 



— varians, Deshayes. 1836. Nouv. Ed. de Lamarck, p. 352. 



_ _ Von Buck. 1834. Uber Terebrateln ; and 1838, Mem. Soc. 



Geol. de France, vol. iii, p. 135, pi. xiv, fig. 4. 



— — Pusch. Polens Palseont., 1837, p. 12, pi. iii, fig. 3. 



— — Bronn. Lethea Geog., 1837, pi. xviii, fig. 4, and Index 



Pal., 1848, p. 1254. 



— socialis, Morris. Catalogue, 1843. 



— varians, B'Orb. in Murch. Russia, vol. ii, p. 480, pi. xlii, figs. 14, 



17, 1845. 

 Rhynchonella varians, B'Orb. Prodrome, vol. i, p. 376, 1849. 



Diagnosis. Shell inequivalved, somewhat irregularly triangular, of the size of a hazel 



