AUCELLA. 71 



1896. Aucella Keyserlingi, A. P. Pavloiv. Ibid., vol. lii, p. 550, pi. xxvii, fig. 3. 



1899. G. Maas. Zeitschr. d. deutsch. geol. Gesellsch., vol. 



li, p. 249. 



1900. — A. Wollemann. Die Biv. u, Gastrop. d. deutsch. u. 



holli'ind. Neocoms (Abhandl. d. 

 k. preussisch. geol. Land., N. P., 

 pt. 31), p. 56, pi. ii, figs. 6—9. 



1901. J. F. Pompeckj. Neues Jalirb. fur Min., etc., Beil.- 



Bd. xiv, p. 319, pi. xv, figs. 3, 6, 

 8—10, 13, 14, 17, 18, 20, 21. 

 1903. A. Wollemann. Zeitschr. d. deutsch. geol. Gesellsch., 



vol. lv, p. 34 (Briefl. Mitteil.). 



Description. — Shell of moderate size, oblique, Avith more or less triangular out- 

 line and rounded margins, higher than long, inflated. Umbones prominent, at the 

 anterior end of the hinge-line, almost touching, curved inwards and forwards. 



Eight valve convex in the neighbourhood of the umbo, but usually flattened 

 elsewhere. Anterior ear close to the umbones, triangular, convex, narrow where 

 united to the rest of the valve, with a deep and narrow bvssal sinus. Posterior 

 ear longer, but indistinctly limited. 



Left valve much more convex than the right valve, especially in the dorsal part, 

 somewhat compressed posteriorly ; greatest convexity between the umbo and the 

 postero-ventral extremity. Umbo more prominent than in the right valve. Ears 

 indistinctly limited. 



Both valves ornamented with many narrow, concentric lamellce which are 

 placed more or less vertically to the surface and are separated by broad, flat 

 interspaces. The lamellae occur at fairly regular intervals, but the distance 

 between them varies on different parts of the shell. They curve gently on the 

 median part of the valve, but bend more sharply in passing on to the anterior 

 and posterior parts, where they become closer to one another. The lamellae 

 have often disappeared from the parts near the umbones. 



Measurements : 



(1) (2) (3) (4) 



Length 31 . 28 . 24 . 18 mm. 



Height 39 . 32 . 30 . 24 „ 



Thickness . — . 16 . 16 . 12 „ 



(1—4) Claxby Ironstone, Claxby. 

 Affinities. — See Aucella volgensis (p. <> l .>)- 



Type. — The specimens figured by Pavlow are in the Sedgwick Museum. 

 Distribution. — Claxby Ironstone (zone of Belemnites lateralis) of Claxby. 

 Speeton Clay (zone of Belemnites jaculum) of Speeton. 



