241' Mr. II. Scelcy on Ammoniies 



slowly. The flat sides, so slightly converging as to be almost 

 parallel, are half as high again as wide. The ventrum is hori- 

 zontal, and rounds into the side. The shallow and open 

 umbilicus shows that, up to the first, the whorls were smooth. 

 Here there are fourteen thickenings, which rapidly become 

 moderately elevated tubercles. A rib given off from each of 

 these bifurcates a little way up the side, but is very little 

 elevated. One or both of the branches reach the back, ter- 

 minating in a tubercle not larger than that at the umbi- 

 licus. In the last quarter-whorl the ribs are curved towards 

 the mouth, and are obliterated in the upper part of the whorl. 

 The dorsal tubercles in the same space rapidly get smaller, be- 

 coming oblique thickenings; they form a row of twenty-five. 

 The last half-whorl is devoid of septa. These shells are as un- 

 sym metrical as any in the young state, but become finally nearly 

 symmetrical. The square dorsal lobe, more than half the width 

 of the back, has a notch on each side and two small terminal 

 branches. The dorsal saddle is of the same width, and mesially 

 cleft. The upper lateral saddle is rather narrower, with a notch 

 on each side and three terminal branches. The other parts are 

 similar, but much smaller. There are two small accessory 

 lobes. 



The dorsal tubercles are alternate, and the back slightly convex. 

 There are other specimens, one-fourth larger, with the mouth 

 perfect and as wide as high, with the shell inflated. The dorsal 

 angle is obtuse and rounded; the side rounds more noticeably 

 into the ventrum. 



I believe these shells to be variations from A. auritus. 



Ammonites Vraconensis, Pictet & Campiche, T. C. Ste. Croix, 

 pi. 31. fig. 1. 



Inflated, few-whorled ; whorls two-thirds-embracing, with 

 (diam. 3 inches) flat sides and a nearly flat back. The sides 

 converge, giving the mouth something of the outline of an in- 

 verted flower-pot. At one-third up the side is a row of eight or 

 nine large elevated spines, the space interior to which rounds 

 down to the whorl it embraces, and is smooth. From each 

 spine commonly arise (three or) four ribs_, which extend up the 

 side to the margin of the back. At the angle where the side 

 and back meet is a row of tubercles about three times as nu- 

 merous as the umbilical spines, and in these the ribs terminate, 

 commonly two, sometimes but one, in each ; so that there are 

 generally one or two free ribs between all the spines. Many of 

 the ribs are straight ; but the hinder one of the two, meeting in 

 a dorsal tubercle, necessarily has a bend in its upper third. The 

 dorsal tubercles of the two sides are not opposite, but alternate, 



