130 SYSTEMATIC PALEONTOLOGY 



several variable;, usually obscure, longitudinal undulations cross the 

 revolving ribs, granulating them and often reticulating the surface. 

 Labium expanded, grooved and cancellated. Labium with two, distinct, 

 oblique folds and numerous striae, continuations of the external revolv- 

 ing lines. Canal short, recurved. 



Length, 17 mm.; width, 8 mm. 



Occurrence. — Aquia Foemation. 1 mile southeast of Mason Springs. 



Collection. — Maryland G-eological Survey. 



Superfamily RACHIGLOSSA. 

 Family OLIVIDAE. 



Genus OLIVULA Harris. 



Olivula sp. 



A single specimen was found which gives little doubt of its generic 

 character. It is probably distinct from 0. staminea (Conrad). In the 

 imperfect condition of the specimen it is impossible to assign it to any 

 species, new or old, and a figure would show no determining characters. 



Length, 20 mm.; width, 6 mm. 



Occurrence. — Nanjemoy Foemation. Popes Creek. 



Collection. — Maryland Geological Survey. 



Family VOLUTIDAE. 



Genus VOLUTILITHES Swainson. 



Volutilithes peteosus (Conrad). 

 Plate XXI, Figs. 4, 5, 5a. 



Voluta petrosa Conrad, 1838, Fossil Shells of the Tertiary, No. 3 [1st Edit.], p. 20. 

 Voluta petrosa Conrad, 1835, Fossil Shells of the Tertiary, No. 3 [2ud Edit.], p. 41,. 



pi. xvi, fig. 2. 

 Athleta inonieyi Conrad, 1853, Proc. Acad. Nat. Sei. PWla., vol. vi, p. 449. 

 Volutilithes (Athleta) tuomeyi Clark, 1895, Johns Hopkins Univ. Circ,, vol. xv, p. 4. 

 Volutilithes {Athleta) tuomeyi Clark, 189G, Bull. 141, U. S. Geol. Survey, p. (i5, pi. x,. 



tigs, la, lb. 



Description. — " Shell subgiabrous; body whorl marked with from eight 

 to ten longitudinal folds, terminating on the shoulder in compressed 



