﻿RISSOINA. 



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The late Professor Eugene Deslongchamps (' Notes Paleontologiques,' vol. ii, 

 May, 1889, p. 70) could not be persuaded that Amberleya and Eucyclus were 

 synonymous, and thus he maintained that Amberleya nodosa, M. and L., could not 

 be a Eucyclus. The presence in that species of a slight umbilical excavation 

 was one of his principal reasons for considering that Amberleya and Eucyclus are 

 distinct genera. As so often happens, Amberleya nodosa, the type, is far from 

 being a typical species, and it would have been far more satisfactory if Turbo 

 ornatus, Sow., could be taken for the type, as was done by Deslongchamps in 

 constituting his genus Eucyclus. 



With regard to the relationship of Amberleya, some authors, like Fischer, 

 admit that the various forms grouped under this genus have the appearance of 

 Tectarius, Echinella, and Littorina ; but Fischer considers that the alleged 

 existence of a nacreous layer in the Jurassic Amberleyas proves their affinity 

 with the Turbinidse and the Trochidaa. Of course, if this is the case, the group 

 of small shells which appear to be connected by so many links with Amberleya are 

 wrongly named Littorina ; and that is why, as already stated, this term is only 

 used in a conventional sense. It would save trouble if they were replaced under 

 Turbo; and yet they certainly are not Turbos in the modern restricted sense, 

 although they may belong to the Turbinidse . 



Many of the forms described in the sequel seem to run into each other. 

 Moreover some of the species differ so much at different stages of their growth, 

 especially in the character of the aperture, that one and the same species might 

 well be placed under two distinct genera. (See description of Amberleya ornata.) 



As regards arrangement, exception might be taken to the wide extension of 

 the term Amberleya, adopted in the subjoined classification of Inferior Oolite 

 species. Unless we fall back upon Turbo and Trochus, I do not see how this is to 

 be avoided. The distinction also between Amberleya and " Littorina " is 

 admittedly not a very philosophic one. 



If we attempt to deal with the Amberleya- Littorina group in sections, the first 

 and most important section is that (1) of Eucyclus i where the shell is much 

 turrited, the suture wide, the body- whorl ventricose, and one or more of the 

 spiral belts exceedingly prominent. The Trochus- section (2) contains shells more 

 or less trochiform, but with an ornamentation closely resembling that of 

 Eucyclus. Through the more turbinate and finely ornamented forms of the 

 Eucyclus-section, such as Amberleya densi 'nodosa, a connection is established with 

 (3) the Turbo-section, which presents some extreme forms. The shells of all 

 three sections are rather thin, and exhibit a considerable resemblance in the 

 general style of ornamentation, and frequently also in the changing character of 

 the aperture. 



In the fourth section (4) the shells are thicker, but do not attain to any 



