CTENODONTA. 101 



Pilton, anotlier specimen figured by Phillips as Pullastra antiqua, Sow., from 

 Barnstaple, another from Oroyde, a specimen of the valves in contact from " North 

 Devon," and one showing the hinge from Baggy. In the Porter Collection are two 

 specimens from Pilton. In my Collection are specimens from Saunton Hotel, from 

 the Laticosta Beds of Baggy, from Kingdon's, Shirwell, and from Pouch Bridge. 



BemarJcs. — This species is evidently one of the commoner and more widely 

 spread bivalves of these beds, though, probably from its tenuity, the specimens are 

 almost always defective or distorted. Examples of the extent to which this may 

 go are to be seen from PI. XIII, figs. 1 and 3, the transverseness of which is, I 

 believe, entirely due to artificial elongation. The same causes also often more or 

 less obscure the posterior depression, which seems one of the most distinctive 

 features of the species. Under these circumstances it is extremely difficult to be 

 certain that it is more than a variety of Gt. antiqua, or to define the distinguishing 

 points if they really exist. After an examination, however, of numerous specimens, 

 including the originals of Sowerby's and Phillip's figures, I am inclined to the 

 opinion (1) that the two are probably distinct; (2) that they both belong to 

 Palasoneilo ; (3) that Sowerby's Gt. antiqua is to be recognised by its more evenly 

 ovoid form, by its concentric ribs being smaller and more numerous, and by the 

 depression on the posterior region being smaller, weaker, and not so greatly 

 deflecting the margin ; (4) that the present shell seems to be characteristic of the 

 Pilton beds proper, while Gt. antiqua appears to belong to the Marwood beds ; 

 and, lastly, that the specimen Phillips figured as Gt. antiqua, Sowerby, sp., 

 really belongs to Gt. lirata and not to Gt. antiqua, as it shows the same 

 characters, especially the posterior depression, and is a Pilton, not a Marwood fossil. 



The surface of some of the specimens is very well preserved, and shows four 

 or five concentric ridges between each of the major ribs. My impression is that 

 this may be another distinguishing mark where the fossil is suSiciently well 

 preserved to retain it. A cast in my collection from Kingdon's shows that the 

 interior of the shell under the umbo is a good deal pitted, but had no internal 

 sulcus like that belonging to the kindred genus Nuculites. The specimens from 

 the Laticosta Beds show much variation in the number and regularity of the ribs. 



Affinities. — Palaeoneilo Bauliniana, Houault,^ appears to differ only in having 

 more numerous and irregular striations. 



The type species of Palseoneilo, P. constricta, Conrad,^ has much finer striae than 

 either of the Devonshire species, and is more acute behind. P. Jilosa, Conrad,* 

 w^hich approaches nearer in ornament, appears to be more angulated, and its 

 striae are more lamellar, and its posterior depression broader and flatter. 



1 1888, (Ehlert, ' Bull. Soc. Geol. Fr.,' ser. 3, vol. xvi, p. 650, pi. xvi, figs. 4, 4 a. 



2 1885, Hall, ♦ Pal. N. T.,' vol. v, pt. 1, No. 2, p. 333, pi. xlviii, figs. 1—20. 

 8 1885, Hall, ibid., p. 343, pi. xlix, figs. 33—38. 



