177 



Description. — This shell so closely resembles Ammonites Brookii, that 

 I have long suspected it might only be a variety of that species, the want, 

 however, of a good series of specimens of A. Turneri, to enable me to 

 compare it with A . Brookii in different stages of growth, has induced me 

 to retain, for the present, Sowerby's name, and give his description of 

 A. Turneri from the vol. v., p. 75 of the Mineral Conchology. "Depressed, 

 radiated, carinated, a furrow on each side of the keel ; inner whorls 

 exposed ; radii numerous, equal, curved towards the front ; aperture 

 oblong-quadrangular. Volutions about five, the inner ones almost wholly 

 exposed ; the radii are almost straight until they are rather suddenly 

 bent towards the front ; the aperture is less than one-third of the 

 diameter of the last whorl in length. The more exposed whorls, squarish 

 aperture, and differently curved radii, distinguish this from A. Brookii, 

 to which it bears a strong resemblance." 



The septa are very imperfectly preserved in the specimen I have 

 figured, PI. 2, fig. 4, b, represents the dorsal lobe, which is narrow, and 

 nearly as long as the super-lateral lobe. Fig. 4, h, the artist copied from 

 Quenstedt's tab. 3, fig. 19, a; but as this is a young A. ohtusus, and not 

 A. Turneri, as that author supposed, it does not help us in this critical 

 enquiry. 



Affinities and Differences. — The affinities of A. Turneri with A. Brookii 

 are so numerous, and the differences between them so few and inconsider- 

 able, that I consider the question of their specific identity one which requires 

 further consideration ; the affinities are more fully pointed out in the 

 description of A . Brookii. 



Locality a/nd Stratigraphical Position. — The specimen figured was col- 

 lected from a light-coloured clay and limestone in the deep cutting of 

 the Bristol and Birmingham railway, near Bredon, associated with 

 A. Bonnardii, d'Orbigny, A. semicostatus, Y. & B., and several other 

 mollusca, with many fragments of the stems and side arms of Pentacrinus 

 tuberculatum. Miller, and Cidaris JSdwardsii, Wright. 



Ammonites Birchii, Sowerby. (PL 1, fig. 3, a, b.) 



Ammonites Birchii, Sowerby, Min. Conch, vol. 3, p. 121, PL 267, 1820. 

 Planites It Haan, Amm. el Gon., p. 82, No. 2, 1825. 



Ammonites h Quenstedt, Cephalopoda, p. 86, 1849. 



.1 It c;'Or6.,PaLFran.,ter.Jurassique,p.287,PL86,1842. 



Shell compressed, back rounded without a keel ; whorls numerous, 



narrow, slightly involute, sub-rotund ; sides compressed, with numerous 



thick obtuse costce, two tubercles developed on each, which are sharp in 



yoxing, and blunt in old shells ; aperture rotund with flattened sides. 



H 



