INVERTEBRATES. 369 



Trochactseon.* The Carboniferous species of Macrocheilus were doubtless origi- 

 nally handsomely colored shells, since a species described by de Koninck, from 

 the. Carboniferous rocks of Belgium (il/. maculatus), retains rows of large 

 rectangular, oblong spots, like some of the modern Mitras and Cones. 



The elongated species of this genus are not always easily distinguished from 

 certain forms of Polyphemopsis, especially when the aperture and columella 

 cannot be seen. They, however, differ entirely in their thickened inner lip, 

 usually provided with an obtuse fold, and in generally having the body whorl 

 proportionally larger. They also differ in having a larger aperture, which is 

 more rounded below. From Loxonema, with which they are sometimes 

 confounded, they are distinguished by their more callous inner lip, with 

 its fold or ridge, their usually less elongated spire, and smooth surface.^ 



So far as known to us, the genus Macrocheilus seems to have been introduced 

 during the Devonian epoch, and attained its maximum development during the 

 deposition of the Carboniferous rocks, particularly the Coal Measures. Prof. 

 King refers to it an elongated shell from the Permian rocks of England (J/. 

 symmetricus), resembling some species, apparently of this genus, from the Coal 

 Measures of the Western States, excepting that its columella seems not to be 

 thickened, and its lines of growth have a flexure more like we see in Loxonema, 

 to which genus it may more properly belong. We cannot remember any Triassic 

 species, though it is not improbable that the genus was represented during that 

 epoch. 



Mr. A. Adams refers to this genus a recent shell from the coast of Japan, 

 under the name M. japonicus {Ann. and Mag. Nat. Hist., 1860, p. 407), and 

 says it agrees almost exactly, in form, with M. acutus, but has no fold on the 

 columella, which is thickened. Notwithstanding its close resemblance to the 

 type of the genus Macrocheilus, we may reasonably doubt its identity with that 

 genus, of which we have no authentic examples from the Jurassic, Cretaceous 

 or Tertiary rocks. 



It is not improbable that the rules of nomenclature may require that the 

 name of this genus shall be changed, because it had been previously used for 

 a genus of Coleoptera. Mr. Conrad's genus, Streptostylus, was evidently- 

 founded upon internal casts of one or two species of this genus ; and his name 

 might be retained for it, in case it should be thought desirable to make a 

 change, were it not for the fact that it was proposed for another group of Mol- 

 lusks by Beck, in 1837. " 



* See Am. Jour. Sci., xxxv, sec. series, p. 89, for a paper on the Actxonidm, to which 

 family the genus Macrocheilus seems to belong. 



■j- By some error, Chenu figures Pleurotomaria Yvanii, Leveille, a spirally striated 

 shell (Conch., i, p. 228), as Macrocheilus acutus, Sowerby. 



47 Sept. 27, 1S06. 



