MARYLAND GEOLOGICAL SURVEY 307 



Venus campechiensis var. tetrica (Conrad). 

 Plate LXXX, Fig. 2, Plate LXXXI, Fig. 2. 



Venus tetrica Conrad, 1838, Fossils of the Medial Tertiary, p. 7, pi. iv, fig. 1. 

 Mercenaria tetrica Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. .574. 

 Mercenaria tetrica Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 9. 

 Venus campechiensis Dall, 1903, Trans. Wagner Free Inst. Sci., vol. iii, pt. vi, pp. 

 1315, 1317, 1318 (in part). 



Description. — " Shell triangular, cordate, ventricose, moderately thick, 

 with crowded concentric very prominent laminae; posterior side subcunei- 

 form, extremity angulated; summits very prominent; lunule defined by 

 a deeply impressed line. 



" This shell has nearly the outline of V. mercenaria, but may be distin- 

 guished by its very prominent laminse of nearly equal elevation on every 

 portion of the disk." Conrad, 1838. 



Length, 122 mm.; height, 100 mm.; diameter, *2 7 mm. 



Occurrence. — St. Mary's Formation. St. Mary's Eiver. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



Venus campechiensis var. mortoni (Conrad). 

 Plate LXXVII, Figs. 1, 2. 



Venus 3Iortoni Conrad, 1837, Jour. Acad. Nat. Sci. Phila., vol. vii, 1st ser., p. 251. 

 Venus Mortoni Conrad, 1838, Fossils of the Medial Tertiary, p. 8, pi. v, tig. 1. 

 Venus suhmortoni d'Orbigny, 1853, Prod. Pal. Strat., vol. iii, p. 108. 

 Mercenaria Mortoni Holmes, 1858, Post-Pleiocene Fossils of South Carolina, p. 34, 



pi. vi, fig. 12. 

 Mercenaria submortoni Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 574. 

 Mercenaria submortoni Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 9. 

 Venus campechiensis Dall, 1903, Trans. Wagner Free Inst. Sci., vol. iii, pt. vi, pp. 



1315, 1317, 1318 (in part). 



Description. — " Shell cordate, inflated, thick and ponderous, with 

 prominent recurved concentric laminae, more elevated on the anterior and 

 posterior margins; ligament margin arcuate; umbones prominent; lunule 

 large, cordate, defined by a deep groove; posterior extremity slightly 

 emarginate; cavity of the cartilage profound; teeth large, prominent, 

 grooved ; muscular impressions very large ; inner margin regularly crenu- 

 lated." Conrad, 1837. 



The shape and width of the hinge area and the elevation of the beak 

 and general shape of the shell are much like var. cuneata of the older de- 

 posits at Jones Wharf, 



