242 



off from the ridge to the row of tubercles, and jjresents a series of oblique 

 undulations occasioned by the vanishing of the ribs. The spire is 

 composed of subquadrate whorls : in a specimen, 5| inches in diameter, 

 there are six whorls visible; on the outer whorl are 37 ribs; on the 

 second, 30; on the 3rd, 29; on the tlurd, 29; so that in this example 

 the number of the ribs increases with l;he number of the whorls. The 

 aperture is quadrate, rather higher than wide, a little enlarged at the 

 spire, and sinuous above where it is marked by the central keel, the 

 sulci, and lateral carinse. (PI. 4, fig. 2 b.) 



The septae are symmetrical, foliated on each side, and divided into 

 three lobes, and three saddles formed of unequal parts, fig 2 c. Dorsal 

 lobe, narrow, one-third longer and a little wider than the superior-lateral 

 lobe, having on each side five slightly unequal digitations. Dorsal saddle, 

 one-foui-tli wider than the superior-lateral lobe, and divided into three 

 unequal pai'ts by two unequal accessory lobes. Superior-lateral lobe, 

 a little longer than wide, has three foliated branches on each side. 

 Lateral saddle, nearly double the width of the superior-lateral lobe, 

 divided into many unequal lobes. Inferior-lateral lobe, nearly as wide as 

 the superior-lateral, and divided into numerous unequal digitations. 

 A uxiliary saddle, half the size of the superior-lateral lobe, divided into 

 several unequal folioles. Auxiliary lobe, narrow, descending much lower 

 than the others, and formed of two branches, the one external, and the 

 other inferior. The line of the central ray passing by the dorsal lobe 

 cuts the superior-lateral lobe. 



Affinities and Differences. — This Ammonite strongly resembles A. 

 Bucklandi, Sow. ; it is distinguished, however, by having the whorls 

 more quadrate, and the general form being more angular ; the 34 to 36 ribs, 

 have each a tubercle near the dorsal border, from whence they curve 

 sharjjly forwards towards the sulcus. In A. Buchlo,ndi there are about 

 24 ribs, which gradually disappear on the dorsal border, and there are 

 no tubercles near the angle of the sulcus. It is distinguished from 

 A . obtusus, to which it has a general resemblance, by having narrower 

 whorls, tuberculated ribs, and a flatter back. 



Locality and Stratigraphical Position. — This species has been found in 

 the Zone of Ammonites Bucklandi, (Lower Lias,) near Lyme Eegis and 

 Charmouth, on the coast of Dorset; near Bath; in the deep cuttings of 

 the Bristol and Birmingham railway, near Defibrd, Bredon, Cheltenham, 

 and Gloucester ; and in other localities in the Vale of Gloucester, as by 

 Coombe Hill, Highnam, and Berkeley. The War^Hck Museum contains 



