Z PROCEEDINGS OF THE NATIONAL MUSEUM vol. V4 



The Calvert formation constitutes the lower part of the Chesapeake 

 group. The material composing this formation consists of dark-gray 

 or olive sandy, usually diatomaceous clay. 



The Choptank formation, where recognized, overlies the Calvert. 

 The materials composing this formation consist of dark-brown rather 

 soft sand and greenish-gray clayey sand alternating with indurated 

 sandstone layers. 



The St. Marys formation is divided into three parts. The lower 

 part, or stratum A, consists of a nearly unfossiliferous dark sandy 

 plastic clay. The overlying fossiliferous parts are divided into 

 two fauna! zones — zone 1, or Bulliopsis qyuadrata zone, constituting 

 the lower fossiliferous part, and zone 2, or CrassateTlites iiieridionalis^ 

 the overlying part. 



The Yorktown formation is separated into two faunal zones — zone 

 1, or Pecten clintonius zone, for the lower part; and zone 2, or 

 Turritella alticostata, for the overlying part. 



Zone 1 includes, in part, the " Murf reesboro stage " of Olsson.' The 

 term Murfreesboro is preoccupied, being used by Safford and Kille- 

 brew ^ to designate the lowest limestone of the Central Basin of Ten- 

 nessee. As the fauna of this zone is more closely related to the fauna 

 of the Yorktown formation than to that of the St. Marys formation, 

 I have placed the zone as the basal part of the Yorktown. 



Zone 2 of the Yorktown formation is again divisible into three 

 minor divisions. The lower part underlies the f ragmental beds ; the 

 middle part, the f ragmental beds; and tlie upper part overlies the 

 fragmental beds and represents the latest deposit of the Yorktown 

 formation in Virginia. 



DESCRIPTIONS OF NEAV SPECIES* 



Class GASTROPODA 



CLATHRODRILLIA? BELLOIDES RUSHMERENSIS, new subspecies 



Plate 1, figure 4 



Shell small, rather solid, moderately slender, prominently axially 

 and finely spirally sculptured, and consisting of six remaining 

 whorls — nucleus broken away. Whorls exjDanded medially, con- 

 stricted at the sutural zone. Suture appressed. Anal fasciole wide, 

 shallowly depressed, undulated anteriorly by the rising ribs. Axial 

 sculpture of (on the body whorl, nine) strong, rounded, protractive 



^ Olsson, Axel, Bull. Amer. Paleontology, vol. 5, pp. 155-163, 1917. 



2 Safford, J. M., and Killebrew, .T. B., Elements of Geology of Tennessee, p. 125, 1900. 



3 The photographic illustrations were made in the laboratory of the United States 

 Geological Survey by Mr. W. O. Hazard and the retouching of the prints by Miss Frances 

 Wieser of the section of illustrations of the same bureau. 



