536 B. BuUen Newton — Egyptian Lower Tertiary Shells. 



latter it is separated by its rounder and more fan-shaped contour, 

 the closer arrangement of its costse and consequently narrower 

 grooves. In the adult stage the summits of the ribs show a decided 

 angularity, suggesting affinities with P. carinatus. On the early 

 stages of the ribs a minute nodulose character is present, somewhat 

 resembling P. solariolum of Mayer-Eymar ^ from the Egyptian 

 Eocenes. 



Eemaeks. — The shell appears to be fairly common, occurring in 

 a soft cream-coloured chalky rock as well as in a reddish-brown 

 matrix of a marly character. The specimens are, however, rarely 

 well preserved, being chiefly impressions ; associated with them are 

 some obscure plant remains, a small Area {A. SJsnaensis, n.sp.), and 

 other mollusca of a fragmentary nature. Professor Mayer-Eymar's 

 name is associated with this shell in acknowledgement of his 

 important researches on the geology and paleeontology of Egypt. 



Horizon. — Lower Eocene (Libyan Series). 



Distribution. — Egypt: Hills west of Jebel Zait, western shore 

 of the Gulf of Suez (28a to 30a) ; and right bank of the river 

 Nile opposite Esna (49c). Coll. Geol. Surv. Egypt (No. 628, 

 Box Nos. 28a to 30a ; No. 1,003, Box No. 49c). 



Genus SPONDYLUS, Linnteus. 

 Systema Naturae, 1758, ed. x, p. 690. 

 Type. — S. gr^deropus, Linnteus. 



Spondylus ^gyptiacus, sp. nov. (PI. XX, Figs. 4-6.) 



Description. — Shell subovate, inequivalve, nearly equilateral, 

 inflated at the summit ; lower or right valve the largest and most 

 convex, with usually a depressed, adherent surface at the umbo ; 

 valves ornamented with numerous fine radial ribs (between fifty 

 and sixty), which are rounded or acute according to preservation, 

 smooth, and separated by simple grooves without striations; sculpture 

 more or less zoned, with from eight to ten more distinctive ribs 

 than the rest ; ribs apparently without spines ; internal characters 

 not seen. 



Dimensions (with valves united). 



Height 43 ram. 



Length 38 ,, 



Diameter 27 ,, 



Remarks. — According to the researches of Bellardi^ and ZitteP 

 two species of Spondylus have been recognized from the Egyptian 

 Eocenes, viz., S. rarispina, Deshaj'es, and S. BouauUl, D'Archiac, 

 a form originally described from the Nummulitic of India. Both, 

 however, differ from the present shell, not only in outline, but 

 in their primary ribs being furnished with conspicuous spines ; 

 S. Bouaidti, in addition, exhibiting transverse striations between the 



1 Journ. Concbyliologie, 1888, pi. xiv, fig. 5, p. 328. 



- Bull. Soc. Geol. France, 1851, ser. ii, vol. viii, p. 261. 



2 Palaeontographica, 1883, vol. iii, p. cvii. 



