and Tery inconstant variety, it will be preferable to adopt Zieten'i 

 well-known name A. Aalensis, which represents the typical form 

 though not an adult one. D'Orbigny's figures of A. Aalensis represent 

 the aged and young conditions of the typical form, his figures of 

 the septa are more complicated and the lobes more produced than is usually 

 seen even in old shells. The first three or four volutions have large, 

 elevated, nearly straight, sometimes fasciated ribs, which gradually become 

 less conspicuous until they are not distinguishable from the faintly marked 

 folds of growth, in old specimens these costated volutions are nearly 

 concealed by those succeeding, which are almost plain. 



The second variety " Costula" Ammonites costula, Reinecke, A. Aalensis 

 costula, Quenstedt, A. Adceon, d'Orb. (?) is usually more tumid than the 

 typical form, and has narrow, curved, distant, and nearly regular costoe, 

 which disappear towards the keel ; in the adult state the costoe become 

 irregular, and gradually disappear. This is a small rare variety. 



The third variety " Regularis" Ammonites regula/ris, Simpson, from the 

 sands at Blue Wick, and from Frocester Hill, is also a small variety, 

 and more tumid than the typical form ; it has acute elevated curved 

 radii much more closely arranged than in costula, and in some instances 

 they are nearly regular and equal for an entire volution, in other instances 

 the costoe are less conspicuous and more unequal, but they are scarcely 

 fasciated, it is comparatively rare. Simpson places this form in the Middle 

 Lias, which is an error, as I have ascertained from comparing the original 

 specimen in the Scarborough Museum with other examples from Blue Wick. 



The fourth variety " Comptus, " Ammonites comptus, Reinecke, is 

 distinguished in the young state by fine closely arranged sigmoidal radii, 

 which are fasciated at occasional intervals by folds of growth, subsequently 

 they are not fasciated and gradually disappear ; Reinecke's figure represents 

 the young condition of this variety which accompanies the other varieties 

 in the Upper bed of the Sands at Frocester Hill. 



The fifth and largest variety "Moorei," Ammonites Moorei, Lycett, figured 

 and described in my little work, " The Cotteswold Hills," is more nearly 

 allied to comptus than to the other varieties in the characters of its radii, 

 which, however, are not fasciated, they are very fine, acute, but not 

 altogether regular or equal ; in large specimens more than half of the last 

 volution is destitute of ornament. A comparison of Zieten's figure of 

 A. Aalensis with that of A. ifoom will form my best excuse for having in 

 the first instance failed to discover the affinity of the two forms ; their 

 dissimilarity is indeed so great that it will require some faith in the 

 foregoing statements to realize the idea of their specific unity in 

 the absence of a good series of connecting specimens. The varieties of 

 A. Aalensis may therefore be arranged into the following groups, 



