AEGOCERAS BOUCAULTIANUM. 329 



figures ; the lines, whicli are certainly developed in the outer lamina of the shell, appear to 

 resemble the punctated lines I have described in the shells of Arietites obtusus and Ariet. 

 stellaris^ and which also exist on Ae^. planicosta, to be described in the sequel. These 

 beautiful and graceful falciform lines in the outer lamina of the shell form a new feature 

 in the history of this species, and become a good diagnostic character between it and 

 Aeg. Cliarmassei, to which it otherwise stands in close relationship. The falciform 

 lines on the surface of the shell, and the tubercles on the sides of the siphonal area, serve 

 to distinguish Aeg. BoucauUianum from other Lower-Lias congeneric forms. The 

 largest specimen sent, was collected from the zone of Aeg. Birchii at Port-Royal, 

 and the small specimen came from Menetreux, near Semur (Cote-d'Or). One of 

 the large specimens of this species, contained in the Semur Museum, has the entire 

 shell most beautifully ornamented with the fine punctated lines which I have so 

 imperfectly described from the weathered specimen now before me. 



The group Angulati requires a more detailed study than has been given to it. The 

 neglect has probably arisen from the difficulty experienced in assembling a sufficient 

 number of examples of the dififerent forms for critical comparison ; figures, however good, 

 will not suffice for this purpose, as nothing short of the fossils themselves can supply the 

 structural evidence necessary to arrive at a definite conclusion. Dr. Oppel grouped 

 Am. atigulatus, Schloth., colubratus, Ziet., catenatus. Sow., Moreanus, d'Orb., Charmassei, 

 d'Orb., Leigneletiiy d'Orb., angulatus depressus, and compressus, Quenst., as varieties of 

 angulatus^ Schloth. A careful study oiAeg. catenatum, angulatum, Cliarmassei^ however, 

 has disclosed, as we have already seen, certain structural characters in each of these forms 

 which appear to justify the separation proposed by d'Orbigny. This series of forms 

 stands very distinct from those of the section PsiLO>fOTi, which preceded them in the Lias 

 sea, and probably derived their parentage from Aeg. incultum, Beyr., and Aeg. Palmai, 

 Mojs., in Trias time. I have not yet satisfied myself as to the true ancestry of Aeg. 

 angulatum, which has a form so distinctly different from all the Psilonoti that it is 

 impossible to confuse it with any form belonging to that series. Here we must range, 

 likewise, Aeg. catenatum, Sow., Charmassei, d'Orb., Boucaltianum, d'Orb., and lacunatum, 

 Buckm., all of which exhibit many characters in common, and many diSerences in detail 

 of minute structure by which they are separated from each other. 



Professor Hyatt, in his ' Genetic Relations of the ANGULATiDiE,' ^ remarks that they 

 form a group precisely equivalent to Discoceratid^, or to the whole of the Falciferi. So 

 far as their involution and the general parallelism of their characteristics are concerned, they 

 are simply a very highly accelerated series, in which there are as great differences between 

 the extreme forms as there is between the extreme forms of the Discoceratidj3 or of 

 many other groups composed of more numerous forms with less abrupt modifications. 



Aeg. catenatum at Semur occurs below Aeg. Cliarmassei and Aeg. Leigneletii in the Aeg. 

 angulatum-bed, and in the Aeg. tuberculatum-bed is succeeded by Aeg. BoucauUianum. 

 1 Proceedings of the Boston Soc. of Nat. Hist., vol. xvii, p. 15—33, May, 1874. 



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