AEGOCERAS STRIATUM. 379 



— " This is a rare and singular shell from the Hawsker shore, armed with a double row 

 of spines placed on angular ridges on the sides. Between the two rows are irregular ribs, 

 running from the inner knobs to the outer, and each generally splits into two elevated 

 ribs on the back, partly fimbriated, whereas on the inner part of the whorl, within the 

 interior row of knobs, the ribs are replaced by numerous slender striae. The space 

 between the rows is also slightly striated; the whorls are few, the outer being 

 very large, and the central part forming a deep cavity or umbilicus ; interior whorls 

 are much concealed ; the back is rounded, but seems to acquire an angle behind, near the 

 aperture, which therefore approaches the heptangular. On account of this we may name 

 this species Am. heplangularis." It is very evident from this description that Young 

 had clearly discerned the specific distinction between this shell and A. Ilenlei/i, a diff'er- 

 ence which has been entirely overlooked by many subsequent authors. Sir Roderick 

 Murchison, in his ' Geology of Cheltenham,' figured this fossil as Am. Cheltienensis, and 

 subsequently d'Orbigny, in his ' Paleontologie Fran^aise,' gave a very fine figure of it 

 imder the name Am. licnleyi, whilst he correctly quoted Reinecke's figure and species, 

 and erroneously confused it with Sowerby's Henleyi in his synonymy of the species. 



The shell is largely inflated and ornamented longitudinally with innumerable small 

 fine striations ; the sides of the shell have throughout two rows of large tubercles, the 

 inner row connected with the spiral suture by numerous fine striae, and the outer with 

 the inner row by short, straight, split ribs. The outer row of tubercles is developed 

 on the margin of the siphonal area, and from each tubercle proceeds the strong band 

 which passes across the area, and joins its fellow, on the mesial line from the opposite 

 side. The siphonal area is convex, depressed, and boldly sculptured with transverse 

 bands and intermediate concave depressions. The outer whorl is very large, and nearly 

 conceals the penultimate whorl, which is more than one half involute. The whorls in 

 this Ammonite increase very rapidly in every dimension, and they consequently leave a 

 narrow, deep umbilicus, in which less than half of the inner whorls are visible, the 

 internal row of tubercles decorating the margin of the spire. 



The lobe-line is very complicated. The siphonal lobe (fig. 5) is a little shorter and 

 narrower than the principal lateral lobe, and ornamented with three branches. The 

 siphonal saddle as wide as the principal lateral lobe, terminates in three foliations of oak- 

 leaf forms. The principal lateral lobe terminates in three large branches, with lateral 

 ramifications. The lateral saddle terminates in two unequal foliations. The lateral lobe 

 is oblique, smaller than the principal, but has a similar figure. The auxiliary saddle 

 has three contracted foliations, and the auxiliary lobe ends in several digitations. 



The aperture is large, wide, and expanded, and has a rounded or a heptangular form. 



This species assumes in early life the specific form and ornamentation I have 

 described, and does not pass through any apparent metamorphoses so peculiarly charac- 

 teristic of Ae(j. Henleyi and Aey. heterogenmn. The longitudinal striations so distinctive 

 of the species are found only in the structure of the shell, and are not observed on the 



