mmonites plicatilis soweroy, 1818. 
CEPHALOPODA Ammonites plicatilis 
Sowerby, 1818. 
Original description 
(1818. — Sowerby, Min. Conch., Vol. II, p. 149). 
« AMMONITES plicatilis. TAB. CLXVI. 
« Spec. CHar. Discoid, radiated ; sides flat ; front round, plain in the 
centre ; volutions exposed ; radii numerous, equal, straight, furcate ; aper- 
ture squarish, with rounded angles. 
« The radii on this Ammonite, from their straightness, closeness, and regularity, have 
much the appearance of artificial plaiting or crimping; they do not branch until they begin 
to turn over the front, in the centre of which they are nearly obliterated ; they are some- 
times simple and less frequently trifid. The septa are acutely sinuated. The thickness is 
about one-fourth the diameter : the aperture is somewhat longer than wide. 
« À sandy Stratum, containing beds of sandy Limestone, at Dry Sandford and Marcham, 
N. W. of Abingdon, produces this shell; I am indebted for the use of the specimen figured 
to the Rev. William Buckland. Several other Ammonites occur in the same Stratum, 
among them is A. concavus of tab. 105 ,, : most of them have lost the shell; the present 
is only a cast of the inside, it has a few crystals of Carbonate of Lime about it » 
… « The inside casts of this are so well preserved, with regard to the sinuosities, that 1 was almost induced to 
add a fresh figure of it from some elegant specimens lent me by the Rev. W. Buckland. » 
OBSERVATIONS 
This type was refigured natural size and redescribed by me in the Quarterly Journal of the 
Geological Society, Vol. LX, p. 55, PI. IX, 1904. The suture-line is now re-drawn. 
Sowerby does not record the exact locality from which the type came, but the species is 
generally regarded in England as the zone-fossil of the Upper Corallian. It belongs to the 
genus Perisphinctes. 
In the original description (line 11) À. concavus should be À. excavatus, for the latter is the 
species figured on tab. 105 and it is a Corallian form, while the former comes from the 
Inferior Oolite. 
1904. M. Healey. 
PALAEONTOLOGIA UNIVERSALIS. — 51° 
