198 CRETACEOUS LAMELLIBRANCHIA. 



1884. Janira atava, 0. Weerth. Die Fauna des Neocom. im Teutoburg. Walde 



(Palaeont. Abhandl., vol. ii), p. 54. 

 1887. — — L, Mallada. Sinops. Espec. F6s. en Espafia, vol. iii, Cret. 



infer. (Bolet. Com. Mapa geol. Espafia, 



vol. xiv), p. 129. 

 — — neocomienrir, Mallada. Ibid., p. 130. 



1891. atava, /. Felix. Verstein. mexican. Jura- u. Kreide- Format. 



(Palseontographica, vol. xxxvii), p. 171. 



1895. — — G. Maas. Zeitschr. d. deutsch. geol. Gesellsch., vol. xlvii, 



p. 269. 



1896. — — A. Wollemann. Ibid., vol. xlviii, p. 841. 



1899. Vola (Janira) atava, D. J. Anthula. Kreidefoss. d. Kaukasus (Beitr. z. 



Palaeont. u. Geol. Osterr.-Ungarns 

 u. d. Orients, vol. xii), p. 71. 



1900. Janira atava, A. Wollemann. Die Biv. u. Gastrop. d. deutsch. u. hol- 



li'ind. Neocoms (Abhandl. d. k. preus- 



sisch. geol. Land., N. F., pt. 31), p. 50. 



? — Vola atava, G. Muller. Verstein. des Jura und der Kreide (Deutsch- 



Ost-Afrika, vol. vii), p. 551, pi. xxiv, fig. 4. 



? Non 1883. Pecten (Neithea) atava, W. Keeping. Foss., etc., Neoc. TJpware and 



Brickhill, p. 107, pi. iv, fig. 6. 



Description. — Shell roughly triangular, often slightly inequilateral ; ventral 

 margin very convex, with deep incisions between the main ribs ; postero-dorsal 

 margin concave, antero-dorsal nearly straight. Anterior ears long, triangular. 



Right valve convex, with the umbo considerably incurved and sharp. The six 

 main ribs are prominent and rounded, and are separated by much broader inter- 

 spaces, which are concave or somewhat flattened. In the interspaces and on the 

 sides of the main ribs, from three to twelve small, slightly raised ribs usually 

 occur, but are absent in some cases; the central ribs are rather stronger than the 

 lateral. Numerous fine, equal, regularly placed, concentric ridges cross both ribs 

 and interspaces; they are parallel with the ventral margin of the valve, and con- 

 sequently bend ventrally in crossing the main ribs, and curve dorsally in the inter- 

 spaces. Similar concentric ridges are also present on the ears. 



Left valve flattened, sometimes slightly convex or slightly concave, with six 

 main ribs, which are rounded and somewhat more prominent than those on the 

 right valve. Interspaces broad and deep, with small ribs. Concentric ornamentation 

 similar to that on the right valve. 



Measurements : 















(i) 



P) 



(3) (4) 



(5) (6) 



(7) 



(8) 



(9) 



Length . 24 . 



23 



22 . 21 



20 . 20 . 



1!) 



. 17 



21 mm 



Height . 80 . 



28 



. 20 . 25 . 

 (1—8) Upware. 



20 . 25 . 

 (9) Faringdon, 



25 



22 



■ 27 „ 



