164 DEVONIAN FAUNA. 



Museum. It evidently belongs to the same species as the specimen which Phillips l 

 refers to it, but which Davidson 2 unites with Bh. reniformis, Sowerby, only differing 

 from it by the possession of a low arching fold. On the other hand, the second 

 Devonian specimen figured as Rh. reniformis by Davidson 3 appears more likely to 

 belong to Eh. Phillipsii, Davidson. 4 From the present form all these specimens 

 differ by their wide and nearly straight hinge-lines, and by the character of their 

 folds. Whether, therefore, Rh. subdentata be a synonym of Eh. reniformis or not, 

 it is certain that the present species is distinct from both. 



3. RnyNCHONELLA LATICOSTA, Phillips, sp. Plate XX, figs. 3, 3 a, 4. 



1841. TEREBBATTJLA LATICOSTA, Phillips. Pal. Foss., p. 85, pi. xxxiv, fig. 153. 

 1865. KHYNCHOJTELLA LATICOSTA, Davidson. Brit. Foss. Brach., vol. iii, p. 61, 



pi. xiv, figs. 1 3. 



Locality. It occurs abundantly in a bed about 1 foot thick, which is exposed 

 in a small cave under the cliff near the wall that bounds the south side of Baggy 

 promontory. It is represented in the various collections by specimens which are 

 always defective and contorted. 



Size. A specimen measures 40 mm. wide. 



Remarks. Of this handsome and distinct species I have unfortunately been 

 unable to obtain any specimens that will yield a satisfactory figure. Its beak 

 appears to be prominent and only moderately incurved, and to have long dental 

 plates. The fold and sinus seem low, rounded, and not strongly defined, with five 

 or six ribs on the former, and four or five in the latter. The ribs are strong, and 

 reach quite to the umbo, but appear rounded and not much elevated. In the 

 dorsal valve is a median septum reaching about halfway forwards. The margins 

 of the valves are rounded in. 



Affinities. It appears widely different from our other Devonian species. 



Rh. Pengelliana, Davidson, 5 from Looe, is still larger, and has more ribs on the 

 fold. The Carboniferous Uh. ? Carringtoniana, Davidson, 6 has feebler and more 

 numerous ribs. 



3 1841, Phillips, ' Pal. Foss.,' p. 90, pi. xxxv, fig. 164. 



2 1865, Davidson, 'Brit. Foss. Brach.,' vol. iii, p. 62, pi. xiii, fig. 7. 



3 Ibid., fig. 6. 



4 1882, Davidson, ibid., vol. v, p. 43, pi. ii, fig. 14. 



6 1865, Davidson, ibid., vol. iii, p. 61, pi. xii, figs. 8, 9. 



6 1863, ibid., vol. ii, pt. 5, p. 227, pi. xxiii, fig. 22 ; and pi. liii, figs. 1, 2. 



