246 JSOCEEDIKQS OP THE e^EOtOGHCAL SOCtETt. [Jatl. 22, 



preserved. In a number of the species the adult forms are wholly 

 unknown, while in others the young or fragmentary specimens have 

 received different names from the adult or complete forms of the same 

 species. 



A. Deshayesii, Leym. — ^This Ammonite, which is a very variable 

 one, is confined, I believe, to the upper division of the Speeton Clay, 

 where it is by no means rare. It is the A. fasicostatus of Phillips, 

 while the A. curvinodus of the same author is probably only one of 

 the numerous varieties of it. 



A. hij)mnatus,Wi\M&msoii, MS. This is a large and well-marked, 

 though undescribed species. It characterizes the Middle Neocomian 

 at Speeton, and is also abundant in the Tealby series of Lincolnshire. 



A. Sj)eetonensis, Y. & B. — This is the most abundant of the 

 Speeton Ammonites. It includes the A. venustus and the A. con- 

 cinnus of Phillips, as well as two other well-marked varieties, one 

 a more inflated and coarser-ribbed form than A. concinnus, and the 

 other more compressed and with finer ribs than A. venustus. All 

 these forms pass into one another by insensible gradations ; none of 

 them occur, so far as I am aware, either above or below the Spee- 

 tonensis-beds in the Yorkshire deposit. The same group of forms 

 is found at Potton, and in the Lower Neocomian of South-eastern 

 France. 



A. Noricus, Schloth., Eom. — This is certainly the A. Neocomiensis 

 of D'Orbigny. It is by no means a rare shell at Speeton, and re- 

 ceived from the late Mr. Bean the MS. name of ^. regalis. In the 

 zone which is characterized by this species are a number of varieties 

 of it, which were considered to be species, and received the MS. 

 names of A. munitus, A. fuyxillatus, &c. "When a suficient num- 

 ber of specimens is examined, they are found to pass into the normal 

 form of ^. Noricus by insensible gradations. Several of D'Orbigny's 

 Neocomian species of Ammonites are certainly only varieties of this 

 species. The form with a broad smooth back, which is found at 

 Speeton, and which is certainly the A. consobrinus, D'Orb. {A. eva- 

 liclus, Bean, MS.), may also be only a variety of the same species. 



A. Astieriamis, D'Orb. — This is a most variable form. D'Or- 

 bigny figures two very dissimilar specimens as possibly male and 

 female shells. There seems to be every gradation between the com- 

 pressed form, A. multiplicatus, Eom. (very well marked specimens 

 of which occur at Speeton) , and the well-known highly inflated form. 

 Although this species is most abundant in the beds which I have 

 named after it, scattered specimens of it appear to occur higher in 

 the series. 



A. Nisus, D'Orb. — This is undoubtedly the A. planus of Phillips, 

 though not of Mantell. Mantell's shell is only one of the numerous 

 varieties of the Gault species A. sjplendeyis. The form referred to 

 by Professor Phillips as " ]ike parvus " is probably only the yoang 

 of A. Nisus. 



A. rotula, Sow. — This is the A. Youngii (Bean, MS.), Y. & B. 

 I have obtained specimens reaching 3^ inches in diameter, and also 

 others which are intermediate in size, and which enable us to form 



