288 
NATJTJLOIDEA. 
Fig. 63. 
Nautilus Cantahri^iensis. — a, lateral view of a cast (No. 68510), showing the 
curved sutures and the shelly plug filling the umbilicus ; 6, peripheral 
view of the same. Drawn from a specimen in the British Museum. 
Natural size. 
Casts of the umbilicus seem to indicate that the shell had faint 
longitudinal striae crossed by the lines of growth ” {JuTces- 
Browne.') 
Remarhs. Many casts of this well-marked species are contained 
in the British Museum. Nautilus Cantahrigiensis is easily distin- 
guished ivom N.Clementinus^ d’Orb., which it most nearly resembles, 
and its lowermost layer always contains an accumulation of the phosphatic 
nodules, commercially known as ‘ coprolites.’ 
“The Cambridge Greensand has been traced north-eastwards from Harling- 
ton in Bedfordshire into Cambridgeshire, and has everywhere been found to 
present similar characters. Its constitution varies slightly in different places 
according as one or other of its several ingredients — clay, marl, or glauconite — 
happens to predominate, but everywhere the green grains become fewer and 
fewer in an upward direction, so that it gradually passes into the greyish beds 
of the Chalk Marl. 
“ For a long time it was considered as Upper Greensand, and was supposed 
to be the diminutive representative of the series of greensands, chert-beds, and 
firestones so well known in the south of England ; it has been shown, however, 
that these die out in a northerly direction before the Cambridge Greensand 
commences, and it is much more probable that this is the homotaxial equivalent 
of the so-called Chloritic Marl, which is generally separated from the Upper 
Greensand by a band of phosphatic nodules,” 
