406 H. Bullen Newton — Egyptian Newer Tertiary Shells. 



sandy matrix, accompanied by crystals of selenite, and beneath some 

 beds containing vertebrate remains {Hippopotamus, etc.). On account 

 of their striking resemblance to Italian forms they are regarded as of 

 Pliocene age. 



HoBizoN. — Pliocene (probably Astian) : in the Lake Deposits of 

 Wadi Natrun at the hill known as ' Moluk.' 



Distribution. — Eed Sea, etc. (Recent) ; Tunis, Montpellier, Ehone 

 Basin, Italy (Pliocene), Algeria: Kabylie (Sahelian or Tortonian). 

 Egypt : near Cairo (Fuchs) ; Moluk Hill, Wadi Natrun. Coll. 

 Geol. Surv. Egypt (No. 327, Box No. la). 



Genus UNIO, Eetzius (Philipsson), 1788. 

 Nova Testaceorum Genera, 1788, p. 16. 

 Type, — Mya margaritifera, Linnaeus, 



Unio Willcocksi, sp. nov. (PI, XX, Figs. 1-4.) 

 Unto 'lithophagus' (?), S. P. Woodward: Quart. Journ. Geol. 

 Soc, vol. XX (1864), p. 19 (list name only, no text) ; 

 7ion (Ziegler) Philippi. 



Description. — Shell large, elongate, convex, robust, and orna- 

 mented with concentric growth-lines, which are more or less rugose 

 according to age; posterior region oblique, produced and decreasing 

 in width, anterior margin rounded and short ; ventral area usually 

 with median depression ; umbones anterior, small, eroded, without 

 corrugations ; left valve possesses two divergent cardinal teeth, with 

 two minor ridges between ; posterior lateral teeth elongate. 



Dimensions (of a right valve). — Height, 48 mm.; length, 

 84 mm.; diameter, 17 mm. 



Eemakks. — This species is closely related to the recent African 

 form of Unio Caffer, Krauss (" Die siid Afrikanischen Mollusken," 

 1848, p. 18, pi, i, fig. 14), but diifers in its more elongate shape, the 

 greater length of the postero -lateral teeth, the absence of umbonal 

 wrinkles, and in the more rugose character of its concentric 

 sculpture. One of the present specimens has its umbonal region 

 entirely denuded of the prismatic layer, thereby showing a complete 

 cast of the interior of the early shell in which the pallial line and 

 muscular-scar impressions are clearly discernible. Many years ago 

 Dr. Leith Adams collected some TJnios from the alluvial deposits of 

 Nubia at a height of 150 feet above high Nile at the Second Cataract, 

 which the late Dr. S. P. Woodward identified as TJnio ' litho- 

 phagus ' (?), but gave neither description nor figure. An examination 

 of these shells in the Geological Society's Museum has proved the 

 fact that they are precisely the same as the species now described, 

 but as they differ from U. lithophagus, which is a manuscript species 

 of Ziegler and equivalent to Z7. teretiusculus of Philippi, it is necessary 

 to establish another name, and therefore that of U. Willcocksi is 

 proposed, in recognition of the collector of the specimens, which now 

 form part of the Museum of the Geological Survey of Egypt. It 

 may be of interest to state that TJ. teretiusculus (:= Z7, lithophagus) 

 from the White Nile is of much more slender form, of a nearly 



