INVERTEBRATES. 365 



are associated, while they do not so agree with that of any other univalves 

 known in the same rocks. They are moderately thick and shelly, oval or sub- 

 circular in form, with a lateral or submarginal nucleus, and show not the slight- 

 est traces 0/ the spiral or subspiral stricture, and articulating projection, so charac- 

 teristic of the Neritidse. On the inner side they show a distinct reniform scar 

 of attachment, and on the outside the fine, but distinctly concentric, lines of 

 growth. It will also be remembered that Prof. McCoy figured a specimen of 

 Naticopsis Phillipsi, in his " Carboniferous Fossils of Ireland," with an oper- 

 culum within its aperture, and that it shows no indications of a spiral structure. 



From all that is therefore known in regard to this genus, we are also inclined 

 to doubt the propriety of referring it either to the Naticidse or Littorinid.se, and 

 to believe it will be found to be the type of an extinct family Naticopsidse, near 

 the Naticidse. 



We are not sure this genus occurs in the Silurian rocks ; a few Devonian 

 species seem to belong to it, but it attained its maximum development during 

 the deposition of the Carboniferous deposits. It is also apparently represented 

 by a few species in the Permian rocks. 



Naticopsis nana, M. and W. 



PL 31, figs. 4a, 4b. 



Platyostoma nana, Meek and Woethen, October, 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 463. 



Shell small, subglobose, wider than high, spire much de- 

 pressed; volutions three, increasing very rapidly in size, last 

 one large and ventricose ; suture well denned ; aperture large, 

 broad-subovate, somewhat straightened on the inner side, 

 equaling near seven-eighths the entire length of the shell ; 

 outer lip thin ; inner lip not much thickened ; columella 

 slightly flattened. Surface marked by fine lines of growth, 

 but slightly stronger and more regular near the suture on the 

 upper side of the whorls. Length, (hi 9 inch ;' breadth, 0.21 

 inch ; length of aperture, 0.15 inch ; breadth of ditto, 0.11 inch; 

 apical angle about 123°. 



Since describing this little shell, we have succeeded in clearing the matrix 

 from the columella, which we find presents the characters of Naticopsis. It is 



