Ammonites variocostatus suckiand, 1856. 
ALT ODA Ammonites variocostatus 
Buckland, 1836. 
Original description 
(1836. — Buckland, Bridgewater Treatise, No 6, Geology and mineralogy, Vol. IT, p. 62). 
« Fig. 7. Ammonites variocostatus, (nobis,) an undescribed species of Ammonite from 
the Oxford Clay at Hawnes, 4 m. S. of Bedford. Diameter 9 inches. 
« The name Variocostatus expresses the remarkable change in the character of the Ribs, 
near the outer termination of the air chambers. 
« On the inner whorls of the shell, these ribs are narrow, and highly raised, set close to 
one another, and bifurcated at the back of the shell (from d. to c.); but near the outer 
chamber (b. to a.) they become broad and distant, and the dorsal bifurcation ceases. 
« The edges of the transverse plates are exposed by the removal of the shell from c. to b., 
they appear also at a. d. (Original.) 
« Similar variations in the form of the ribs occur in Ammonites biplicatus and Ammonites 
decipiens. » 
OBSERVATIONS 
This species has been much neglected by recent authors, probably because the original 
figure is so much reduced as to be practically useless. It belongs to the genus Perisphinctes. 
The type was refigured, natural size, and redescribed by me in the Quarterly Journal 
of the Geological Society, Vol. LX, p. 58, PI. XI, 1904, and the following reasons are there 
given for the belief that it came from the Ampthill, not the Oxford, Clay, and is therefore 
of Corallian age : 
10 It is distinctively Corallian in appearance. 
20 Hawnes is only 3 miles north-east of Ampthill, and is near the edge of the band of 
colour indicating Lower Greensand on the Geological Survey maps. Further, the Geological 
Surveyors 1 say that : « Traced beyond Ampthill the boundary of the Oxford and Kimeridge 
Clays is largely concealed for some distance by the Cretaceous rocks. » 
3° It is not pyritized, and T. Roberts ? remarks that in the Ampthill Clay « (fossils) are 
never pyritized and on this account the clay is easily distinguished from the underlying 
Oxford Clay. » 
The suture line has since been more exposed and is now redrawn. 
Hawnes is often spelt Haynes. Varicostatus is frequentely written instead of « variocostatus », 
but it is not such good Latin, for it really means : « having bow-legoed ribs » (Lat. varus), 
while « variocostatus » means : « having ribs which change » (Lat. varius). 
1. Mem. Geol. Surv. (The Jurassic Rocks of Britain), Vol. V, p. 138. 
2. The Jurassic Rocks of the Neighbourhood of Cambridge, p. 36. 
1904. M. Healey. 
PALAEONTOLOGIA UNIVERSALIS. — 56* 
