158 SYSTEMATIC PALEONTOLOGY 



Family FISSURELLIDAE. 



Genus FISSURIDEA Swainson. . 

 FiSSURIDEA MARLBOEOENSIS n. Sp. 



Plate XXIX, Figs. 6, 6a. 



Description. — -Shell ovate, depressed; apex anteriorly situated, acute; 

 foramen keyliole-sliaped, anterior to the apex, plane sloping forward; 

 internal callus shaped like the end of a gun-stock, deeply dinted behind; 

 surface sculptured by fine, impressed, radiating lines, with broad and 

 flat interspaces toward the periphery, raised and rounded toward the 

 apex; interspaces doubly alternating in width or height, every fourth 

 being much wider, while of each group of intervening narrower ones 

 that in the middle is slightly wider than the rest; alternation becomes 

 simple on the posterior slope, with double alternation strongest on the 

 anterior slope. 



Length, 17.5 mm.; width, 12 mm.; height, 6 mm. 



Occurrence. — Aquia Formation". Upper Marlboro. 



Collection. — Maryland Geological Survey. 



Class SCAPHOPODA. 



Order SOLENOCONCHIA. 



Family DENTALIIDAE. 



Genus DENTALIUM Linne. 



Dentalium minutistriatum Gabb. 

 Plate XXIX, Fig. 7. 



Dentalium minututr latum Gabb, 1860, Jour. Acad. Nat. Sci. Phila., 2nd Ser., vol. 

 iv, p. 386, pL Ixvii, fig. 46. 



Description. — "Very slightly curved, marked by numerous small lon- 

 gitudinal ribs, all of the same size, no trace of alternation; aperture 

 round." Gabb, 1860. 



This form differs from D. mississippiensis in having finer, non-alter- 

 nate ribbing, and not attaining to so great a size. 



