290 PROCEKDINGS OF TlIK MALACOI.OGICAL SOCIETT. 



Nautilus imperialix is I'eferred by Hyatt ' to liis genus Eutrephoeeras,'^ 

 and Nautilus molcnttamensis st^ems to be referable to the same genus. 



EXPLANATION OF PLATE VIIL 



Nautilus viokaitamensis. — a, lateral aspect of a natural internal cast showing 

 the narrow umbilicus and course of the sutures ; 6, front view of the 

 same showing the position of the siphuncle. Eocene: Mokattam range, 

 near Cairo, Egypt. Drawn from a specimen in the British Museum 

 (Natural History), Geol. Dept., register No. C. 12426. Somewhat 

 enlarged. 



' A. Hyatt, " Phylogeny of an acquired characteristic " : Proc. Amer. Philos. 

 Soc.vol. xxxii. No. 143, p. 559, 1894. 



- A. Hyatt, il)id., p. 555. Genotype : Nautilus dekayi, Morton (Synop. Org. 

 Eem. Cret. Group, U.S., 1834, p. 33, pi. viii, fig. 4). Hyatt states that in 

 this genus " There are no annular lobes at any stage of development ", 

 although in his description (p. 559) of EutrepJioceras imperiale (J. Sowerby) 

 he mentions that " This species has an annular lobe which has no 

 connection with the subdorsan siphuncle ", though he adds in the next 

 sentence: "I could not find any traces of these (annular lobes) in the 

 older sutures." Of the examples of the species which the present writer 

 has been able to examine, none shows any annular lobe, even where the 

 height of the whorl is only 5-6 mm. (equivalent to a shell-diameter of 

 8-7 mm.), as in a specimen in the British Museum (No. 68905a) from the 

 London Clay, near Chalk Farm, Middlesex. 



