134 SYSTEMATIC PALEONTOLOGY 



ing threads^ which over-ride botli the longitiidinal and the reYolving 

 folds, the threads showing a tendency to alternate in size; whorls of 

 spire with two, very distinct, revolving folds; major intersecting sets of 

 sculpture giving a reticulate appearance; folds strongly nodular at the 

 intersections; mouth narrow; columella with two, strong, oblique folds; 

 canal long and straight. 



Length, 26 mm.; width, 11 mm. 



Occurrenc&. — Aquia Foemation. 2 miles below Potomac Creek. 



Collection. — Maryland Geological Survey. 



Genus FUSUS (?) Lamarck. 



The following species are referred to the genus Fusus without any 

 claim that their biological affinities are with that genus as now restricted. 

 They belong to that large group of fossils, of approximately fusoid 

 form, but indeterminate generic relationships. 



Fusus (?) suBTENUis Heilpriu. 

 Plate XXII, Figs, i; 2. 



Fusus suhtenuis Heilprin, 1880, Proc. Acad. Nat. Sci. Phila., voL xxxv, p. 371, 

 pL XX, fig. 4. 



Description. — " Shell fusiform, of about seven subangular volutions; 

 whorls ornamented with somewhat obscure longitudinal folds, about 

 twelve on the body whorl, which are cut by several prominent revolving 

 ridges commencing at the shoulder angulation; shoulder of the whorls 

 more or less smooth, with an obscure median revolving line, and a 

 prominent subsutural one; aperture about the length of the spire, or 

 slightly exceeding it, the canal gently curved, moderately contracted, 

 and somewhat expanding at the extremity; outer lip thin, and showing 

 internally the external ornamentation; base with numerous revolving 

 lines, which alternate in coarseness." Heilprin, 1880. 



Very characteristic specimens of this species occur at the locality noted 

 below. 



Length, 35 mm. (restored); width, 18 mm. 



Occurrence. — Aquia Formation. 2 miles below Potomac Creek. 



Collection. — Maryland Geological Survey. 



