Maryland Geological Survey 493 



face marked by three major revolving costse which are flattened on top; 

 in addition to the major costaa there are lower, angular, revolving ribs 

 siuated as follows : one between the lower suture and the first major costa, 

 one between the first and second costas, two between the second and third 

 costse, and two between the third major costa and the upper suture. In 

 the casts the sutures are rather close, especially between the lower and 

 larger volutions; the lower volutions are more or less quadrangular in 

 cross-section, the upper ones being rounder, due undoubtedly to the 

 internal thickening of the shell with age." — Weller, 1907. 



Occurrence. — Matawan Formation. Opposite Post 236, Post 218, 

 Chesapeake and Delaware Canal, Delaware. Monmouth Formation. 

 ? Cayots Corners, north end of Fredericktown Bridge, Cecil County, 

 Maryland. 



Outside Distribution. — Monmouth Formation. Navesink marl, New 

 Jersey. 



Family SOLARIIDAE 



Genus SOLARIUM Lamarck 



[Prodrome, vol. i, 1799, p. 74] 



Type. — Trochus perspectivum Linne. 



Shell solid, perforate; outline subdiscoidal to depressed-conic; whorls 

 numerous, regularly increasing in size ; periphery rounded or carinate ; 

 dominant sculpture of simple or beaded spirals; aperture semi-elliptical 

 to subquadrate; columella usually straight, simple; outer lip thin and 

 sharp; umbilicus funicular or scalar. 



Solarium was most abundant in the Eocene and the recent species, the 

 " sun-dial " shells, are relatively few in number and are restricted to the 

 warmer waters. 



In the absence of the nuclear characters it is difficult to separate the 

 members of this genus from those of Euomphalus, but it seems probable 

 that the Solaria occur as early as the Jurassic. 



Etymology: Solarium, sun-dial. 

 32 



