86 BRITISH CRETACEOUS BRACHIOPODA. 



acute, entire, and but little incurved ; foramen small, surrounded by a deltidium in two 

 pieces ; beak ridges well defined, the hinge line not encroaching on that of the dorsal 

 valve ; lateral margins slightly flexuous ; the frontal edge of the ventral valve indenting 

 more or less that of the dorsal one. External surface ornamented by a number of simple 

 radiating plaits, from 30 to 40 on each valve. 



Length 12, width 15, depth 10 lines. (This species at times attains somewhat larger 

 dimensions.) 



Obs. In 1811, Parkinson simply mentioned the name Terebratida sulcata, without 

 description or figure. And in another paper, read before the Geological Society in 1818, 

 but published only in 1821, we find the same name repeated, as follows : 



"Fossils in the Blue Marl. Terebratula sulcata, found near Dover, Folkstone, 

 and Cambridge," but no figure or description is given, so that this appellation is in 

 reality equivalent to a MS. denomination, and the author may have intended the shell for 

 the one afterwards named T. Mantelliana by Sowerby, and which is found in those 

 localities. 



In the ' Geology of Sussex,' p. 130, 1822, Mantell likewise describes a Rhychonella 

 by the name of sulcata, from the Chalk of Hamsey and Stoneham in Sussex, but also 

 without figure, and to this species the name T. Mantelliana was subsequently appended by 

 the author of the ' Min. Con.,' that of Ter. sulcata being retained for another shell found 

 abundantly in the Upper Green Sand of Cambridge. 



In 1843, Mr. Morris mentioned Ter. sulcata as from the Gault of Folkstone and 

 Cambridge: and in 1847, M. D'Orbigny describes the Upper Green Sand Cambridge 

 species as that of Parkinson ; considering at the same time Rh. Gibbsiana (Sow.) a 

 synonyme ; but here the learned author of the ' Pal. Franc' seems to be evidently 

 mistaken. The R. Gibbsiana (Sow.) occurs, it is true, in the vicinity of Folkstone, 

 Sandgate, Hythe, &c, but in another bed, viz., Lower Green Sand (Neocomien), and 

 cannot, I believe, be confounded with the Upper Green Sand species, now so well known 

 to collectors as the true (?) R. sulcata of Parkinson. In a catalogue of the Lower Green Sand 

 fossils in the museum of the Geological Society, 1 Professor Forbes stated that R. sulcata 

 occurs in the Lower Green Sand of Hythe, and mentioned as his var. j3, R. parvirostris 

 of Fitton, a view I can hardly admit. Professor Bronn, 2 while adopting the term sulcata, 

 states it to be his opinion that R. depressa (Sow.), inconstans, rostralina, plicatella, 

 and multiformis (Rcemer), as well as T parvirostris and elegans (Sow.) belong all to 

 the same type ; and although perhaps some of the shells mentioned may bear a resem- 

 blance to our Upper Green Sand species, neither R. elegans, parvirostris, nor depressa can 

 I think, with propriety, be united to the Cambridge R. sulcata. 



Rh. Gibbsiana is more triangular in its external aspect, its sinus and fold much more 



1 Quarterly Journal of the Geol. Soc, vol. i, p. 345, 1845. 

 3 Index Pal., vol. ii, p. 1852; 1848. 



