16 



GASTEROPODA. 



\ 



^^^mc-i 



Fig. 396. — Macroeheilus 

 siibcostatus. Devoniau. 



fossil forms belong to the genera Pyramiddla, Chemnitzia, 

 Eulima, Loxonema, and Macroeheilus. 



In Pyramiddla (fig. 397, d) the shell is slender and tiir- 

 reted, and the columellar lip is plaited. The genus is doubt- 

 fully represented in the Cretaceous, but there are various Ter- 

 tiary and many living species. Odostomia, 

 with a few Cretaceous representatives, 

 but occurring more abundantly in the 

 Tertiary, includes minute turreted shells 

 with a single tooth-like columellar fold. 



Chemnitzia (fiig. 397, g) includes a num- 

 ber of slender, turreted, many-whorled 

 shells, with plaited whorls, and a simple 

 aperture. The genus appears to com- 

 mence in the Permian rocks, and whilst 

 more than one hundred and fifty fossil 

 species are known, the number of the 

 living forms is very small. Many of the 

 shells, however, included under this head, 

 are of very doubtful affinities. 

 Etdima (fig. 397, f) includes small, polished, elongated 

 shells, with level whorls and a reflected inner lip. Eidimm 

 are of doubtful occurrence in the Carboniferous rocks, are 

 sparingly represented in the Secondary rocks, and are toler- 

 ably abundant in the Tertiaries. 



Loxonema (fig, 397, e) extends from the Silurian to the 

 Trias, but is most abundant in the Carboniferous. The shell 

 in this genus is long and turreted, with convex whorls, 

 which have no spiral band, while the surface is covered with 

 longitudinal, often more or less arched threads or ridges. 

 Macroeheilus (fig. 396) includes thick smooth shells, with 

 convex whorls, an oval, not distinctly notched aperture, a 

 callous inner lip, and an imperforate columella. The genus is 

 mainly or exclusively Devonian and Carboniferous, and no 

 Secondary or Tertiary forms have been detected, though a 

 living Japanese shell has been referred here. The Carbon- 

 iferous Orthonema is allied to Loxonema, and the Solcniseus 

 of the same formation probably also belongs to tliis family, 

 though it has affinities with Fasciolaria. 



