R. Biillen Newton — Egyptian Lower Tertlanj Shells. 533 



Horizon. — Middle Eocene (Mokattam Series). 

 Distribution. — Egypt : Minyeh. Coll. Geol. Surv. Egypt (Nos. 

 844, 848 ; Box Nos. 12^' c, 50c}. 



Genus POTAMIDES, Brongniart. 

 Annales Museum Paris, vol. xv (1810), p. 367, pi. xxii, fig. 3. 

 Type. — P. Lamnrchi, Brongniart. 



PoTAMiDES (allied to) perditus (Bayan). (Pi. XIX, Figs. 3, 4.) 

 Cerithium perditum, Bayan : " Etudes Foss. Nouveaux," fasc. i (1870), 

 p. 41 (= Cerithium Lamar chi, Desbayes non Brongniart, 

 and C. deperditum, Desbayes now Micbelotti). 

 Description. — Sbell witb an elongate, turreted, and acuminate 

 spire ; wborls numerous, convex, deeply sutured, spirally striate, and 

 longitudinally ribbed ; terminal wborl large and basally depressed ; 

 aperture round ; labrum sinuated ; canal sbort. 

 Dimensions. 



Length 12 mm. 



Spiral angle 17°. 



Remarks. — A number of silicified casts of a small Ceritliium-VikQ 

 sbell are determined as being allied to Potamides perditus, a well- 

 known Paris Basin univalve. Tbe specimens, well exposed on tbe 

 surfaces of a lenticular cbert-bed measuring about an incb in thickness, 

 have from ten to twelve whorls sejjarated by a deep suture, and 

 a prominently sinuated labrum. Sculpture has mostly disappeared, 

 but a few examples exhibit two spiral lines in the centre of the 

 whorl, crossed by longitudinal costee. The main difference between 

 this form and the typical species appears to be its very much smaller 

 size, so that a relationship so close would suggest an Eocene age for 

 this particular chert-deposit, although the Egyptian Survey officers 

 are inclined to regard it as belonging to a somewhat later period.^ 



Horizon. — Eocene or Oligocene (?). 



Distribution. — Egypt : VVadi Natrum, lake deposits, north-west 

 of Cairo. Coll. Geol. Surv. Egypt (No. 633, Box No. 37a). 



LiMNJEA, Melanopsis, etc. 



Remarks. — Numerous casts of Limncea, Melanopsis, Potamaclis, 

 Bithynia, etc., ai'e observable in a highly saliferous, white, chalky 

 limestone^ of variable hardness. In its fauna and general lithological 

 features this matrix bears a curious resemblance to the Headon Hill 

 limestone of the Isle of Wight, and even the species, judging from 

 the imperfect condition of the specimens, show a similar facies in 

 both. The molluscan remains are, however, so badly preserved that 

 they do not lend themselves to either accurate identification or 

 description, making it difficult to refer them to any special horizon, 

 although they may temporarily be regarded as doubtfully of 

 Oligocene age. 



^ Information supplied to the writer by Dr. Hume in August, 1898. 



^ Mr. G. T. Prior, of the British Museum, informs me that this matrix is not 

 a dolomite, although referred to as such on the manuscript lists accompanying the 

 collection. 



