Ammonites of the Yorkshire Cornbrash. 65 
Schlotheim in 1813; Nautilus tumidus by Reinecke and A. 
terebratus by Phillips. This Ammonite is of great thickness 
(tumid), is Ir0 mm. wide at the end of the last whorl where the 
body chamber commences, and the height is 65 mm.; the 
diameter across the umbilicus is 145 mm. and the umbilicus is 
only 25.mm., nearly . 
In the small specimen the diameter across the umbilicus is 
45 mm., and the umbilicus is Io mm., or about } of the diameter 
of the shell, besides being so small the umbilicus is very deep, 
the walls being almost vertical. 
The ribs increase on the periphery and decrease towards the 
umbilicus by combination ; on the periphery nearest to the 
body chamber there are four ribs in 23 mm., and at the com- 
mencement of the second whorl six ribs in 23 mm. in the largest 
specimen. 
In the smallest specimen there are four ribs on the outer 
periphery in Io mm., and on the inner six ribs in 7 mm. 
In the adult form there is a gradual failing of the ribs until 
the surface is almost smooth. 
Macrocephalus typicus Blake. This Ammonite is called 
macrocephalus by Zittel and Nikitin, and is figured as such by 
Zittel and Kayser-Lake. The sides are flattened, and the 
umbilicus quite vertical, the ribs enter the umbilical wall 
and curve backwards from the umbilicus to the periphery. 
In this specimen the diameter is 95 and that of the umbili- 
cus I5 mm., or just over 3 of the entire diameter. The height 
of the last whorl near the body chamber is 28 mm., and its 
width 34 mm. 
In a large specimen of this species the height is 56 mm., 
and the width is 98 mm. 
There are four ribs in 23 mm. on the outer periphery, and 
eight on the inner one. 
This handsome species is totally different from the first 
mentioned species, as it is also from the next species. 
Macrocephalites herveyi Sowerby. This Ammonite has not 
flattened, but rounded sides, not globular in appearance as in 
macrocephalus, but really comes between the aforementioned 
two species. The umbilicus is not vertical but nearly so ; 
the diameter of No. I is 110 mm., and the umbilicus is 30 mm., 
or about } the diameter. 
The height of the last whorl next to the commencement of 
the body chamber is 40 mm. and the width 60 mm. 
There are nearly six ribs in 23 mm. at this point and seven 
at the commencement of the second whorl. They do not curve 
so much as in typicus, but are stronger and deeper. 
In No. 2 the diameter is 120 mm. and the diameter of the 
umbilicus is about 30 mm. or } the whole ; the height is 35 mm. 
and width 55 mm. 
1915 Feb. 1. 
