MARYLAND GEOLOGICAL SURVEY 225 



of the whorl with several impressed revolving lines which do not cross the 

 longitudinal ribs; plait small, oblique, situated near the middle of the 

 columella. 



Length (of fragment), 2 mm.; diameter, 0.8 mm. 



Occurrence. — Choptank Formation. Governor Eun (lower bed). 



Collection. — Maryland Geological Survey. 



Superfamily T/ENIOGLOSSA. 

 Family TRITONiD/E. 



Genus TRITONIUM Link. 



Tritonium centrosum (Conrad). 



Plate LV, Figs. 1, 2. 



Bursa centrosa Con. sp. nov. Cope, 1867, Proc. Acad. Nat. Sci. Pliila., vol. xix, 



p. 139. (Name only.) 

 Bursa centrosa Conrad, 1868, Amer. Jour. Conch., vol. iii, p. 264, pi. xxi, tig. 10. 



Description. — " Turrited ; spire elevated ; whorls with granulated 

 revolving unequal lines, and a series of rounded, prominent, closely 

 arranged nodes' on the angle which is situated below the middle of the 

 whorls; body whorl with three distant nodular revolving ribs; the lower 

 one small; columella with transverse irregular plaits." Conrad, 1868. 



The first four or five whorls are polished, and shaped like a Natica. 

 Then the sculpture abruptly begins. This sculpture consists of many 

 granulated revolving lines, which override one to three revolving rows of 

 nodes on and below the shoulder of the whorl, and, which are in turn 

 overridden by a series of microscopic, closely set, revolving lines and 

 lines of growth. 



Length, 28 mm. ; diameter, 15 mm. 



Occurrence. — Calvert Formation. Plum Point, Charles county, 

 near the Patuxent river {fide Cope). 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 IT. S. N"ational Museum, Philadelphia Academy of Natural Sciences, 

 Cornell University. 

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