INSTITUTE OF SCIENCE, PHILADELPHIA. 33I 



Aldrich has described a var. modesta. I am not sure that S. cancellatuni 

 Conr. and 5. cancellatiim Lea are one and the same species, but both belong 

 to the genus Solariella, and Conrad's name has four months priority. 5. 

 exacnum Conr. (Nov., 1833, -i- Delphimda plana Lea -)- 5. delpliimdoides 

 Meyer) is an Adeorbis, and will be further referred to under that genus. ^. 

 graimlatiim Lea, 7i07i Lam., is not a Solarium, and, under the name tricostatum 

 proposed for it by Conrad, should probably be included in the genus Liotia. 

 S. delpliimdoides Heilprin (Proc. Acad. Nat. Sci. Phila. 1880, p. 375, pi. 20, fig. 

 13), not of Orbigny (Moll. Cuba, ii. p. 67, 1842), nor of Meyer (1887), appears 

 to be one of the mutations of S. ornattini. From the Miocene, with the 

 exception of those already spoken of as belonging to it, only S. trilineaUiin 

 Conrad is known. 



Genus DISCOHBLIX Dunker ? 



Omalaxis [pars) Dall, Rep. Blake Gastr., p. 276, 1SS9, not of Tryon or Deshayes. 

 Orbis Lea, Contr. Geol. 1833, not of LacepSde, 1798, nor Philippi, 1836. 



Solarium bifrons Lamarck, upon which the genus Omalaxis (-f Bifrontid) 

 was founded, is different conchologically from such species as Orbis rotella 

 Lea, Omalaxis nobilis Verrill, etc. Dr. Fischer has found that Bifroniia 

 zaficlcea Phil, has a ToriniaAike operculum, and has therefore proposed for it 

 the sub-generic name of Psmdomalaxis. The shell of P. zdnclcea agrees in 

 every respect with that of Lea's Orbis rotella and Verrill's Omalaxis nobilis, so 

 far as its structure is concerned, but, in the latter. Prof Verrill found the oper- 

 culum thin, multispiral, concave externally — in short, like that of a Trochid- 

 Now, it is eminently probable, in this as in other cases, that the American 

 species march together, and we might regard them rather as related to 0. 

 nobilis than to the Mediterranean form. Dunker's Discohelix was founded on 

 a fossil of the Lias, extremely similar to Orbis Lea, and of which we cannot 

 hope to know much more that will definitely settle its position. There would 

 seem to be no good reason why we should not accept the name for the fossil 

 forms of which we cannot know the operculum. The probability is that Dis- 

 cohelix was like its compatriot P. zanclcea, and not like the American forms, 

 but this cannot be positively determined. At most it will be advisable to put 

 the latter in a section of Discohelix, which might be called Discosulis, with D. 

 nobilis as type, and refer to this all our American species. If it should event- 

 ually prove that our species are distinguished from the European forms by 

 tangible characters visible in the shell, the sectional name might be promoted 

 to sub-generic rank. 



This group has been referred by De Gregorio to Cyclogyra Wood, which is 

 founded on a non-moUuscan argillaceous test, perhaps a Rhizopod. OpJnleta 

 Vanuxem is a Silurian form, probably a worm-tube ; neither has any relation 

 to the present type, nor to Skeuea. 



The only species known from our Eocene is Discohelix rotella Lea, of 



