8HEPPARD : MARTIN SIMPSON AND HIS GEOLOGICAL MEMOIRS 301 
It is found in every bed of the upper Lias, but those specimens which are 
obtained from the upper part of this division, are the largest. The 
striated shell is thin, and when removed, the varied angular, and rounded 
forms of the septa are displayed ; which gives to the cast a beautiful 
foliated appearance. On the outer whorl of some large specimens, 
may be observed straight, obtuse, radii, which become obsolete before 
reaching the back ; but in the smaller specimens these are scarcely 
discernible. 
[page 31] II. With a keel on the back. 
a. Outer ivhorl broad. 
54. A. ELEGANS, Sow, 
Much depressed ; \olutions 4 or 5, inner ones tV concealed, outer 
whorl rather more than J the diameter, inner edge sloping or con- 
cave ; radii twice bent, faint ; keel sharp, prominent, entire ; 
aperture triangular • diameter 3 inches. 
This elegant shell is rather abundant in the jet rock and hard shale 
of the upper lias : the shell is thin, and both it and the cast are smooth 
and shining. About \ of an inch from the inner edge of the whorl, is a 
concentric line, in some specimens distinct, in others obsolete. The 
inner edge of the whorls of this group being deeply indented by the 
succeeding whorls, the apertures have more or less the shape of arrow 
heads." 
After his descriptions of 108 species, he gives a short note on 
Malformations." The index is arranged under the heads of : — 
Nautilus. 
Ammonites. J. — Without a dorsal keel or furrow, a. No spines. 
h. Armed. 
„ IT. — Carinated. a. Outer whorl broad. 
b. Outer whorl narrower. 
. ,, III.— Keel between two furrows. a. Furrows slight. 
b. Furrows distinct. 
,, IV. — With a dorr-al furrow only. 
There is a list of forty-two subscribers, among them being W. Bean, 
J. Buckmaii, the Rev. W. Buckland, J. Leckenby, John Morris, John 
PhiUips, the Kev. A. Sedgwick, H. E. Strickland and the Rev. G. 
Young. 
In 1855 appeared Simpson's book entitled :— 
" The Fossils / of the / Yorkshire Lias ; / Described from Nature 
/ with a short outline of the / Geology of the Yorkshire Coast / 
i Illustrated with sections ; / and intended as / A Guide to Strangers / 
