THE AMMONITES OF THE YORKSHIRE 
CORNBRASH.* 
H. C. DRAKE, F.G.S, 
THE Ammonites of the Yorkshire Cornbrash all belong to 
the genus Macrocephalites, of the family Stephanoceratide, 
defined thus: 
Ammonites with numerous ribs, which cross the periphery 
without change, but which tend to unite on either side at some 
point near the umbilicus. 
The Ammonites of this family commence in the Upper 
Lias and are almost confined to the Lower Jurassic, with the 
exception of the genus Macrocephalites which extends to the 
Oxford Clay. The Macrocephali aré found in the Jurassic 
in most parts of the world. 
The name is derived from pi2.K pos, long, xedady, a head. 
The genus is defined thus by Zittel in his Handbook to Paleon- 
tology :—‘ Involute, with broad, rounded exterior, all the 
whorls regularly covered with numerous sharp ribs, which 
divide into two or more near the narrow deep umbilicus. 
Sutures much divided. 
The shell was first figured by Baier in 1757 but not named. 
Schlotheim in 1813 named the shell Ammonites macrocephalus. 
There are five recognised species in the Yorkshire Cornbrash, 
namely, macrocephalus, typicus, herveyt, hudlestont and com- 
pressus. All my specimens come from the well-known Pea- 
cock’s Quarry on the Seamer Road, Scarborough. 
I have obtained macrocephalus, typicus and herveyi in the 
Cornbrash at Red Cliff and in Gristhorpe Bay, but the con- 
dition of the specimens was not good, all being without the 
shell, therefore in the nature of casts. In Peacock’s quarry the 
conditions of deposition must have been different, the rock here 
is about 3 to 4 feet thick, but on weathering the bottom 18 
inches is shown to contain a large quantity of broken up 
carbonaceous matter with sandy grains, and breaks up almost 
like the underlying sandstones, but of a slaty blue colour 
with black patches. In this, and almost at the lowest portion, 
I have found one or two specimens of macrocephalus and several 
like typicus, but all was in the form of casts. The upper 
portion about a foot from the top of the rock is the most 
prolific, out of 52 specimens in my collection macrocephalus 
form 26%, typicus 54%, herveyi 6%, compressus 60%, hudle- 
stont &%.7 
Macrocephalites macrocephalus. This is the species first 
figured by Baier in 1757, and called A. macrocephalus by 
* Read at the Hull meeting of the Geological Section of the Yorkshire 
Naturalists’ Union. 
+ In addition I have placed a typical series in the Hull Museum. 
Naturalist, 
