360 THE LIAS AMMONITES. 



the whorls l)etween are broader and not so high ; like it, however, it is depressed, dis- 

 coidal, and slightly carinated, without a distinct keel ; the sides of the whorls are flattened, 

 and transversely ornamented with from twenty to twenty-four ribs, according to the age of 

 the shell. They commence at a short distance from the spiral suture, and ascend radially 

 straight to the margin of the siphonal area, where they terminate in small prominent 

 tubercles (fig. 1). The area is ridged in the middle, and declines on each side at a low 

 angle. The row of tubercles from the termination of the ribs bounds this region, which is 

 a clear, angulated, and well-defined area (fig. 2). The spire is composed of compressed 

 whorls, flattened on the sides and angular externally, with a sloping riser internally. 

 The aperture is quadrate, compressed on the sides, and arched in the line of the area ; 

 the height is greater than the breadth, and it is wider near the spiral suture than 

 toward the outer margin. 



The lobe-line is extremely complicated. The siphonal lobe is about the same size as 

 the principal lateral, and ornamented on each side with simple digitations, and two 

 branches, of which the last is the most highly ramified. The siphonal saddle, much wider 

 than the principal lateral lobe, is formed of two unequal branches ; the internal is 

 the larger, and is formed of three foliations. The principal lateral lobe divides into five 

 branches, which are bifurcate or trifurcate, and unequally disposed. The lateral saddle is 

 smaller than the siphonal, and divided into two unequal foliations ; the internal is the 

 larger and formed of three foliations. The lateral lobe is oblique, and furnished with 

 four unequal branches. The auxiliary saddle is small, and formed of three leaves, and 

 there are two or three small additional oblique auxiliary lobes. 



Affinities and Differences. — This species very much resembles Aeg. Valdani ; it is, 

 however, a thicker shell, and the whorls are wider and not so high as in that species. It 

 has only one row of tubercles on the sides, and the ribs are straighter, more erect, and 

 prominent, and arise much nearer the spiral suture than in Aeg. Valdani. The lobe- 

 line differs, likewise, in its style of ramification ; the aperture is wider, more angular, and 

 narrower near the spiral suture than at the outer margin, the opposite to the form and 

 dimensions that prevail in Aeg. Valdani. It much resembles some of the young shells 

 of Arietites Saiizeanus from the Arief. BucMandi-beds of the Lower Lias ; the absence of 

 a keel and the ribbing on the siphonal area clearly distinguish the two shells from each 

 other. It resembles Aeg. hrevispina in some respects ; still the absence of a carina in 

 that species affords a diagnostic character between them. 



Locality and Strati graphical Position. — I have collected this Ammonite from the zone 

 of Aegoceras Ibex in the brick-pits of the Middle Lias at Leckhamptom, near Cheltenham, 

 associated with Aeg. Valdani, Aeg. Loscombi, and Aeg. Ibex. It has been found in the 

 same horizon at Munger, near Radstock, by Mr. Tawney, F.G.S. ; in the Aeg. lamesoni- 

 and Ibex-beds at Fenny Compton by Mr. Beesley, F.G.S. ; in beds of the same age near 

 Ilminster, Somersetshire, by Mr. Chas. Moore, F.G.S. ; and between Lyme Regis and 

 Charmouth, Dorset, associated with Aeg. Loscombi, by several collectors. 



