292 THE LIAS AMMONITES. 



Avallon, Yonne. Near Semur, Cote d'Or, many specimens of a large size have been 

 found, and which are now preserved in the Semur Museum. 

 In Germany, Quenstedt records it from Gmiind. 



Arietites Turneri, Sowerby. PL XII, figs. 1 — 6. 



Ammonites Turneri, Sowerby. Mineral Conchology, tab. 452, vol. v, p. 75, 1824. 



Diagnosis. — Shell discoidal, depressed, strongly carinated, with a deep narrow sulcus 

 on each side of the keel ; whorls costated, with forty-two strong, simple, straight ribs, 

 which bend suddenly forward near the back, each rib thickened at the angle ; inner 

 volutions of whorls well exposed ; aperture oblongo-quadrate. 



Dimensions. — Transverse diameter 115 millemetres ; height of the aperture 41 mille- 

 metres, width 38 millemetres ; amount of involution nearly one fourth of the whorl. 



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 to give his 

 description of A. Turneri from 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 ; the aperture oblong- quadrangular. 

 Volutions about five, the inner ones almost wholly exposed ; the radii are almost straight 

 until they bend rather suddenly toward the front ; the aperture is less than one third 

 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. The 

 lobe-line shows the siphonal lobe (fig. 6) long, narrow, and deeply serrated on both 

 sides, and the terminal branch bifurcated. The siphonal saddle is small, ending in 

 two festoons ; the principal lateral lobe (fig. 5) is oblique, and serrated, terminating in 

 three curved digitations ; the lateral saddle is wide, ending in three festoons, with several 

 lobules on each side ; the inferior lateral lobe is oblique like the principal lateral, and 

 about the same size, with serrated sides and a trifid termination ; the lower lateral 

 saddle is much smaller than the upper lateral, and ends in three festoons of unequal 

 size, with a lateral lobule on each side. 



In PI. XII, fig. 4, I have given an accurate drawing of one of Sowerby's original 

 type specimens, now in the British Museum, to show its identity in form with the shell 

 figured (figs. 1 — 3) on the same plate. 



