AUCELLA. 71 



1896. AucELLA Keyseelingi, a. P. Pavloxc. Ibid., vol. lii, p. 550, pi. xxvii, fig. 3. 



1899. — — G. Maas. Zeitschr. d. deutsch. geol. Gresellscli.,vol. 



li, p. 249. 



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



iKilliiiid. Neoeoins (Alihandl. d. 

 k. preussisch. geol. Land., N. F., 

 pt. 31), p. 56, pi. ii, figs. 6—9. 



1901. — — J. F. PompecJcj. Neues Jahrb. fiir 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. G-esellscb., 



vol. Iv, p. 34 (Briefl. Mittcil.). 



Description. — Shell of moderate size, oljlique, with more or Ics.s triangular out- 

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

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



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

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

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

 ear longer, but indistinctly limited. 



Left valve mucli 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 lamelhv wliich are 

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

 interspaces. The lamellfe occur at faii'ly 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 . o2 . 30 . 24 „ 

 Thickness . — . IC . 16 . 12 „ 

 (1 — 4) Claxby Ironstone, Claxby. 

 Acuities. — See Aucella volgensis (p. 09). 



Ti/pe. — The specimens figured by Pavlow are in the Sedgwick Museum. 

 Distribution.— C\a\hy Ironstone (zone of Belenmites lateralis) of Cla.xby. 

 Speeton Clay (zone of Delenmites jaciilnm) of Speeton, 



