431 
These terms and others of the new descriptive nomenclature, of 
which only very few will be used in these pages, because I think it 
will be essential to discuss them further before applying them to the 
descriptions of cephalopodan shells, have been gradually introduced 
in consequence of the labors of Wilder and Gage, in this country, 
and are in a fair way of being adopted in Europe through the 
effort of Franz Eilhard Schulze and others.* 
Terms like ventran, ventrad, ventral, dorsan, dorsad, dorsal, cen- 
tren and centran, and so on, strike one at first as awkward and bar- 
barous, but their utility becomes apparent, as in the case of the 
siphuncle cited above, as soon as one begins to use them, and they 
can be made to have an exact meaning which it is not practicable 
to gain otherwise without the repetition in every description of the 
same explanatory text. 
The shells of Nautiloidea and Ammonoidea are divided by trans- 
verse partitions or septa into what are called ‘‘ air chambers,’’ and 
the intersections or lines made by the edges of these when they 
strike against the inner surfaces of the shell of the whorl are called 
the sutures. Fig. 15 shows the edges of these septa as they would 
appear in Wautilus umbilicatus (Fig. 1, p. 345) if the shell there 
figured had been fossilized, the air chambers filled with infiltrations 
and the outer walls of the last whorl destroyed except in the umbil- 
icus. The outer empty chamber beyond the suture of the last 
septum is the cast of the living chamber. The sinuous edge of 
this is the impression left by the edge of the aperture on the right 
side. This being a cast artificially made, is somewhat more perfect 
than natural casts of the interiors of such forms in the rocks and 
the spreading abutments of the septa against the inner wall are 
broad bands. Usually, in fossils, the upper extremely thin parts of 
these bands have disappeared, leaving only a line below correspond- 
ing to the lower parts of the bands in this figure and more nearly 
representing the thickness of the internal part of the calcareous 
septum. 
*See Wilder, Science, ii, 1881; Wilder and Gage, Anatomical Technology, 1882, and other 
papers. Also Schulze, Biologisches Centralblatt, xiii, Nos. 1, 2, 1893; Hyatt, ibid., Nos. 15, 
16; and again, Schulze, Verh. d. Anat. Gesellech., Versam. Gottingen, 1893, p. 104; and 
reprint of same, Deutsche Zool. Gesell., G6ttingen, 1893, p. 6. 
