PLATE XXY. 
1. Nautilus Dorsalis. ( BacJc-sipJiuncled Nautilus.) Discoidal, umbilicate; inner volutions wholly concealed ; 
sides smooth, rounded ; aperture sub-rotund; sipliunculus situate close to back; septa distinct; umbilicus 
large, deep. 
2. N. Bistrialis. (Doubly-Striate Nautilus.) Discoidal, umbilicate; inner volutions wholly concealed ; sides 
slightly rounded; umbilicus very large, with several spiral striae on margin. 
3. N. Goniolobatus. (Corner-Lobed Nautilus.) Involute, sub-globose, umbilicate; inner volutions wholly 
concealed ; sides smooth, inflated; ambit rounded ; umbilicus small; sutures retroflexed in small, dorsal sinus ; 
first lateral lobe angular; second not traceable. 
4. N. Ingens. (Huge Nautilus.) Discoidal; inner volutions slightly concealed ; sides smooth ; ambit round; 
aperture orbicular; sipliunculus round, situate at one-third length of aperture from ambit; septa many. 
5. N. Globatus. (Globular Nautilus.) V. Plate XXIII., Fig 11. 
(3. N. Biangulatus. (Two-angled Nautilus.) V. Plate XXIII., Fig. 9. 
7. N. Lineatus. (Lineated Nautilus.) Spheroidal, compressed, umbilicate ; inner volutions wholly concealed; 
sides flattisli, obscurely striated transversely; umbilicus small, well-defined ; ambit flat, broad, with spiral, 
concave groove at centre ; aperture rather quadrangular, with deep indentation from preceding volution; 
sipliunculus situate near centre ; septa many, concave, with three, slight, marginal undulations. Diameter 
one-third longer than thickness. 
8. N. Sulcatulus. (Sulcated Nautilus .) Discoidal; inner volutions quadrangular, partly exposed; sides 
smooth, concave towards outer edge, convex towards marginal slope, with many acute, sigmoidal, transverse, and 
a few spiral striae ; volutions quadrangular; ambit concave along centre, bevelled to sides; aperture oblong, 
ten-sided ; sipliunculus situate near outer edge. 
10. N. Elegans . (Elegant Nautilus .) Sub-globose, umbilicate ; inner volutions one-third concealed ; sides, 
with many, transverse, linear, curved, reflexed sulci, dividing surface into flat ribs; aperture obtusely 
sagittate; sipliunculus large, central; septa concavo-convex, entire; umbilicus minute. Greatest diameter, 
12 in.; greatest thickness equal to about twice width. 
11. N. Annularis. (Binged Nautilus.) Discoidal, with large circular annulation ; sides raised; aperture 
very large ; septa remote, slightly curved. 
12. N. Regalis. (Royal Nautilus.) Gibbose, without umbilicus; inner volutions wholly concealed ; sides 
plain, convex ; ambit flattened ; aperture wider than long ; sides expanded, with considerable indentation from 
volution and straight next back. Greatest diameter, 9 in.; thickness, 5 in. 
13. 14. N. Expansus. (Expanded Nautilus.) Sub-globose, umbilicate; inner volutions wholly concealed ; 
sides, with fine, sharp, transverse striae ; back rounded ; umbilicus small, nearly circular ; aperture transverse, 
greatly exposed, laterally, so as to make axis longer than diameter of shell; septa intersect striae; edges nearly 
straight in front. 
15. N. Radiatus. (Rayed Nautilus.) Gibbose, umbilicate; inner volutions one-third inserted; sides 
rounded, with curved, radiating undulations; ambit rounded; umbilicus of fair size, exposing inner volutions 
and edges of septa ; aperture circular, its length and breadth about equal, and exceeding half diameter of disc; 
deeply indented by intrusion of volutions. Greatest diameter, 64 in. 
( 29 ) 
