392 R. B. Newton — Fossils /ro)ii Nubian Sandstone, Egypt. 



prevailing during the period of deposition. The matrix exhibits 

 a light-coloured weathering on the exposed surfaces, and is of minutely 

 oolitic structure. 



Family Aviculidse. 

 Genus INOCERAMUS, J. Parkinson. 



Trans. Geol. Soc. [London], 1819, vol. v, pt. i, p. 55, pi. i, fig. 3. 

 Type = Inoceramus Lamar cki, Parkinson. 



Inoceeamus Balli, sp. nov. (PI. XXI, Figs. 1-3.) 

 Inoceramus Orip.ii, Blanckenhorn MS.: W. F. Hume, "Topography and Geology 

 of the Peninsula of Sinai (south-eastern portion)," Survey Department, Egypt 

 (Cairo), 1906, p. 153 ; John Ball, " Description of the Fii'st or Aswan Cataract 

 of the Nile," Survey Department, Egypt (Cairo), 1907, p. 67. J^on Mantell 

 nee Goldfuss. 



Description (specimen -with closed valves). — Shell of moderately large size, 

 equivalve, sub -quadrangular from the lateral aspect ; valves antero-medially inflated, 

 arched, compressed towards anterior margin, hut considerably more so posteriorly and 

 ventraily ; cardinal line straight, horizontal, nearly equal iu length to the height, 

 longest posteriorly ; posterior and ventral margins rounded, anterior, more or less 

 truncated, sub-vertical ; umbonal region antero-median, incurved, posteriorly inclined, 

 but with probable anteriorly directed summits ; surface of valves with about twenty 

 elevated, prominent, rounded, concentric costae with laterally attentuated ends, 

 divided by furrows of corresponding width ; costive and grooves broaden as develop- 

 ment proceeds, but become lost and insignificant in the area of greatest compression ; 

 extremely fine concentric lineations ornament the surface of the ridges and furrows. 



Dimensions. — Height 120, length 115, diameter 75 mm. 



Hetnarks. — This Inoceramus would appear to belong to the group of 

 which Cripsi of Goldfuss {non Mantell) ^ might be taken as the type ; 

 in fact, the specimen has already been so determined by Dr. Blancken- 

 horn, although important differences exist which would undoubtedly 

 separate it from the species itself. There is the rather quadrangular 

 outline as opposed to the general transversely oval figure of the typical 

 German shell, the presence of the prominent antero-median elevation 

 from the umbonal part downwards, and the more medially situated 

 umbonal area. Chiefly in the well-sculptured costte and grooves does 

 it approximate to the Goldfussian shell. The posterior inclination of 

 the umbonal region, mentioned in the diagnosis, need not necessarily 

 imply that the shell was opisthogyrous, as it is more than probable 

 that were the summits in preservation they would be found assuming 

 the usual anterior direction hitherto associated with the genus 

 Inoceramus. A similar phenomenon may be obseiwed in large examples 

 of /. concentricus, Parkinson, of Albian (= Gault) age, which exhibit 

 the prosogyrous character of the umbones followed by a more oblique 



1 Without attempting a revision of the Inoceramoid shells, it is necessary to remind 

 the student that Orbigny was the first pahieontologist to recognize the importance 

 of separating into two species the forms which Goldfuss had included under Cripsi 

 in the Petrefacta Gerinanice. He therefore substituted Goldfitssianus for Cripsi, 

 because the latter name was preoccupied by Mantell for a shell of different form 

 and horizon (Cenomanian), limiting its application to the example represented by 

 fig. A:d of the Goldfuss plate 112; whilst that of regularis was acknowledged to 

 embrace figs. 4ff, b, c of the same plate (see Orbigny, Pal. Frangaise Terr. 

 Cretaces Lamellibranchia, 1845, p. 517, pi. ccccxi, and Prodrome Pal. Strat., 1850, 

 vol. ii, p. 250). The nomenclature of some of these Senonian Inocerami has been 

 recently under the consideration of Dr. Job. Bohm in the Monatsher. Deutsch. Geol. 

 Ges., 1907, No. iv, p. 113. 



