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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. (Min. 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 Eutrephoceras 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 E. Dekayi and smaller than in E. 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 Dekayi. 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 Eutrephoceras 

 Dekayi except that I could not find any signs of the linguae-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- 



