TEREBRATULA. 15 



bifurcation, smaller plaits appearing between the principal costse, which lying often close 

 to the original ones at their origin, give a false appearance of bifurcation; and draw so near 

 to each other at the margin, that seven or eight may be counted in the breadth of a line, 

 eighty or ninety ornamenting each valve. 



This shell is found in the London clay; the largest specimens I have seen, 10 lines in 

 length, were procured by Mr. Bowerbank from the London clay of Sheppey; it has 

 likewise been met with in other localities. 1 



I have felt embarrassed to decide which name this species should retain, being aware 

 that the term striatula had been applied by Dr. Man tell, in 1822, to a cretaceous species, 2 

 but which name was however only a synonym, the shell having received that of striata, in 

 1821, from Wahlemberg. 3 Subsequently Sowerby, as well as many other authors, 

 indiscriminately adopted Dr. Mantell's name, both for the cretaceous and the species under 

 consideration; I have therefore thought it advisable, to avoid a new name, to adopt that 

 of striatula exclusively for the Tertiary species, and retaining that of striata for the Chalk 

 shell. We may likewise observe, that from the description and figures given by Mr. 

 Morton, 4 of his Ter. lacryma, we should conclude our London clay species distinct from the 

 American one. 



Fig. 16. Specimen from the London clay of Sheppey, in the collection of Mr. 

 Bowerbank. 



16°. An enlarged illustration. 



Genus — Terebratula, Lhoyd. 1699. 5 



Shell inequivalve, equilateral, elongated, transverse or circular; exterior smooth, rarely 

 striated or plaited; valves generally convex, with or without sinus, corresponding to a 

 mesial fold in smaller valve. Front straight or sinuated : beak always truncated by an 

 apicial, emarginate, or entire foramen ; deltideum in one or two pieces; internal ribbon- 

 shaped lamella (partly supporting the ciliated arms), attached only to the crura, short or 

 elongated, and more or less folded back on itself; animal fixed to submarine bodies, by 

 muscular fibres passing through the foramen ; structure perforated. 6 



1 M. Deshayes has, within the last few years, found, in the Calcaire Grossier of the neighbourhood of 

 Paris, young specimens of a shell, which is probably the same as our British species ; but, from the great 

 similarity presented by specimens at that age, it is very difficult to decide as to identity. 



2 ' Geol. of Sussex,' pi. xxv, figs. 7, 8, 12. 



3 'Wahlemberg Petref.,' pi. vi, 1821. 



1 J. S. Morton, 'Synopsis of the Organic Remains of the Cretaceous Group of the United States,' 

 pi. xvi, fig. 6; and pi. x, fig. 11. According to Sir C. Lyell, Viscomte D'Archiac, and M. D'Orbigny, 

 T. lacryma would belong to the age of the London Clay; and it is placed by M. D'Orbigny in his 

 'Terrain Parisien Prodrome,' vol. ii, p. 396. 



5 ' Lithophylaci Britannici Ichnographia.' London, 1699. 



6 See Introduction, and Part III, p. 26. 



C 



