NAUTILID^. 
369 
the sharp aud strong median keel on its under surface, and the 
sharply keeled borders, separating the latter from the upper surface. 
Two less conspicuous keels are seen on each side of the median 
one, extending posteriorly from the beaks ; these make five keels in 
all : hence the name. From the Neocomian of the South of France 
(jN’o. 73814 a). The figures are drawn of the natural size, from a 
specimen in the British Museum. 
Fig. 80. 
a, view of the inner side of an uppar mandible ; h, view of the outer side of an 
upper mandible, showing on one side ili) remains of the horny lamina 
appearing as a red stain upon the chalk ; c, lateral view of the same speci- 
men ; d, view of the dentated margin of the apical part of a lower man- 
dible {of. Nautilus pompilius, Fig. 76, a, h). a (No. 98207) is from the 
Ohalk of Offham Pit, Lewes, Sussex ; 6, o (No. 39788) is from the Lower 
Chalk of Maidstone, Kent ; d (No. 37869) is from the Lower Ohalk of 
Dover, Kent ; e, view of the inner side of an upper mandible ; /, lateral 
view of the same specimen, showing the ridged posterior portion ; g, outer 
side of the same. From the Upper Greensand of Devizes, Wilts (No. 
88876 a). All the specimens are drawn of the natural size from specimens 
in the British Museum. 
Remarhs. The Chalk forms (fig. 80, a-d) closely resemble those 
of the Gault {cf. fig. 79, a-d), both iu shape and internal markings. 
In both there is a very thick pad or swelling developed on the 
internal aspect of the upper mandible, extending for about two 
thirds of the distance from the base towards the apical extremity* 
PART II, 2 B 
