NO. 1312. SYNOPSIS OF THE YENEIUD.E— BALL. 377 



VENUS MERCENARIA var. CANCELLATA Gabb, i860. 



A rare variety, described from the ^Miocene, and occasionally found 

 living-, in which the medial smooth space of the type is concentricallj- 

 di\'ided into Hat riblets by shallow grooves, the riblets being also 

 radially sulcate. 



VENUS MERCENARIA var. RADIATA Dall, 1902. 



Similar to the last, except that the smooth medial area is not con- 

 centrically sulcate. 



VENUS MERCENARIA var. ALBA Dall, 1902. 



In this form the interior is like notata^ and the exterior destitute of 

 colored lineation. 



VENUS CAMPECHIENSIS Gmelin, 1792. 



Chesapeake Bay and southward to Cuba; westward to Texas and 

 southward to Yucatan, near low-water mark. Fossil from the Miocene 

 to recent faunas. 



This is the largest species of the famih" and th(> most ponderous, 

 characterized by high inflated beaks, blunt ends, white shell, f recjuently 

 with zigzag brown lineation in the 3'oung externally, and a surface 

 sculpture of dense, low, thin concentric lamellation. The young usu- 

 ally begin in a somewhat quadrate form, with more distant lamellation, 

 without a purple border internalh^, but sometimes a purple flush in 

 the cavit}^ of the beaks. It passes through a series of mutations anal- 

 ogous to those of V. niercenaria. 



The young shells about 2 inches or so in diameter have been named 

 VemiK cdJciircd b}^ Philippi, 1844-, V. tenuilamellatd Sowerby, 1853, 

 and V. fid (J II I'd n.'i 'Tvjon^ 1865. Gmelin's type was also an adolescent 

 shell. The recent adult has been named V. prepared Say, 1822; Y. 

 fiiortoiu Conrad, 1837, and V. alhoradiata Sowerby, 1853. To the 

 various nmtations exhibited by the species m the fossil state the fol- 

 lowing names have been given: V. tdrlcn Conrad, 1838; V. 2>ei' magna 

 Conrad, 1838; V. cajxm Conrad, 1844; Y. siihnortoni Or))igny, 1852; 

 Mercenarl<i. ohtasa Conrad, 1866; M. ouneafa Conrad, 1868, and 2L 

 carnll)ienf<ix CV)nrad. 1875. 



VENUS CAMPECHIENSIS var. ALBORADIATA Sowerby, 1853. 



Shell with l>road l)rownish rays on a paler ground. 



VENTIS CAMPECHIENSIS var. QUADRATA Dall, 1902. 



Shell small, (juadrate, thin, compressed, and unicoloi'ate, usually 

 yellowish white. 



