342 SYSTEMATIC PALEONTOLOGY 



Height, 9 mm. ; diameter, 14 mm. 



Occurrence. — Calvert Formation. Plum Point, 3 miles south of 

 Chesapeake Beach. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum, Philadelphia Academy of Natural Sciences, 

 Cornell University. 



Solarium amphitermum Dall. 

 Plate LVIII, Figs. 4a, 4b. 



Solarium amphitermum Dall, 1892, Trans. Wagner Free Inst. Sci., vol. iii, pt. ii, 

 p. 330, pi. xxii, figs. 16, 16a. 



Description. — " Shell moderately elevated, large, solid, with a blunt 

 periphery and about seven whorls; nucleus sinistral, overturned and im- 

 mersed in the succeeding coil ; upper surface with a transverse sculpture 

 of regularly spaced, impressed lines in harmony with the fiexuous lines 

 of growth; periphery marked by a strong, broad, blunt rib cut by the 

 impressed lines so as to carry squarish nodulations. This is separated 

 from a similar but less pronounced rib behind by a deep, very narrow 

 groove ; the surface hence to the suture may have one or two fine obsolete 

 spiral raised lines, or may show merely the transverse impressed lines 

 which sometimes gather at the appressed suture; base flattened, inside 

 the rounded edge of the peripheral rib is a small beaded spiral ; umbilicus 

 small, bordered by a stout rib with about twelve denticles, outside of 

 which is a smaller, undulated, flatfish rib with a deep, narrow groove on 

 each side; between this and the peripheral cord the surface is nearly 

 smooth, or with a few fine obsolete raised lines transversely sculptured 

 with impressed radiating lines strongest near the umbilicus; aperture 

 subquadrate, wider than high, the end of the umbilical rib, when perfect, 

 grooved and guttered. Max. diam. of shell 18.5 ; of umbilicus 5.0 ; alt. 

 of shell, 10.0 mm 



" S. trilineatum is smaller, proportionately more ele- 

 vated and has a sharp periphery." Dall, 1892. 



Height, 10 mm.; diameter, 18.5 mm. 



Occurrence. — Choptank Formation. Greensboro. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



