509 
special description is necessary. It must be noted, however, that 
the shell was absent, so that no comparison of the ornamentation 
could be made. 
EUTREPHOCERAS IMPERIALIS. 
NAUTILUS IMPERIALIS, Sow. (fiz. Conch., Pl. xiii, Figs. 13-16). 
Loc., Isle of Sheppy and Isle of Wight, Tertiary. 
Pl. xiii, Figs. 14-16. 
In this interesting Tertiary species the siphuncle is subdorsan 
even in the apical chamber, as is shown in Fig. 14, and it clings to 
this position throughout the nepionic stage. The form does not 
seem to differ materially from that of Awtrephoceras Dekayi. ‘The 
umbilical perforation is of about the same form and size, that is to 
say, it is as small as is practicable to afford room for the shell to 
turn and has a depressed comma shape. ‘The external umbilici are 
more open than in &. Dekay¢ and smaller than in &. Faxoense. 
The ornamentation is quite distinct. In the nepionic stage there 
are longitudinal ridges and transverse bands, but these are never so 
prominent as in Dekay?. In what I suppose is the neanic stage 
these still persist, but are so fine that their intersecting lines, with 
minute depression in the checker-board-like spaces between them, 
give a punctate aspect to the surface when viewed with a cross 
light. 
The specimens from the Isle of Sheppy, supposed to be identical 
with this species, shows the presence of a dorsal furrow in the 
opposed dorsi of the meta- and paranepionic volutions, Fig. 16, 
and the very small size of the perforation. 
This species has an annular lobe which has no connection with 
the subdorsan siphuncle. I could not find any traces of these in 
the older sutures. The sutures resembled those of Autrephoceras 
Dekayi except that I could not find any signs of the linguee-form 
dorsal saddles in the centre of the dorsal lobes. 
Nautilus. 
Before beginning the brief notice of this genus, which I propose 
to give, I desire to return thanks to Henry Brooks, whose observa- 
tions and drawings have contributed so largely to the interest of 
this paper. These are also noticed in connection with the figures 
themselves. I am also deeply indebted to Dr. Charles E. Beecher, 
of New Haven, who has loaned me a series of beautiful prepara- 
