494 Systematic Paleontology 



Solarium monmouthensis n. sp. 

 Plate XIII, Fig. 7 



Description. — Shell suborbicular, spire very low and smoothly rounded, 

 the contour not interrupted at the sutures ; whorls flattened from five to six 

 in number, regularly increasing in size; the suture lines coincident with 

 the periphery ; shell substance apparently rather heavy but decorticated 

 so that no trace of the original sculpture is discernible ; sutures quite 

 deeply impressed; body whorl acutely angulated at the periphery, the 

 base feebly convex near the aperture ; aperture probably trigonal, although 

 its outline is partially concealed by the silicified matrix; character of the 

 umbilicus also concealed. 



Dimensions. — Altitude 5 mm., maximum diameter 14.5 mm., diameter 

 at right angles to maximum diameter 12 mm. 



The type is the only representative of the genus in Maryland. Although 

 it is impossible to determine with certainty the affinities of shells of this 

 type, in which the nuclear characters and the operculum have been lost, 

 yet the general outline suggests Solarium much more strongly than it does 

 any of the Euomphalidce. 



Occurrence. — Monmouth Formation. Two miles southwest of Oxon 

 Hill on Mrs. Linton's branch, Prince George's County, Maryland. 



Collection. — Maryland Geological Survey. 



Family XENOPHORIDAE 



Genus XENOPHORA Fischer de Waldheim 

 [Tab. Syn. Zoogn., 1808, p. 113] 



Type. — Xenophora conchliophora (Born). 



Shell low, trochiform, but never nacreous; imperforate or narrowly 

 umbilicate; whorls flattened, armored with agglutinated extraneous 

 objects ; base subconic, or flattened with a sharp, peripheral keel ; aperture 

 obliquely quadilateral. 



The persistence of this genus from the mid-Paleozoic to the Eecent 

 bears testimony to the efficacy of the extraordinary device by which this 

 mollusc protects itself. The bulk of the shells and pebbles carried by this 



Etymology: |e> j, a stranger; <pt P u, I carry. 



