292 AXEL A. OLSSON 



with a small anterior lateral tooth in the left valve and its socket in the 

 right. External sculpture formed by distant concentric lamellations frilled 

 by radials. Pallial sinus small and of triangular shape. 



Subgenus YENTRICOLARIA Keen. 1954 

 {Ventricola of most American authors.) 



Type species by orginal designation, Venus rigida Dillwyn. Recent, 

 Florida and the Caribbean. 



Shell generally large, rotund, solid, the surface sculptured with coarse, 

 concentric lamellar riblets, their crests sharp or reflexed and marked with 

 fine, concentric threads in their interspaces; there are no radials. Lunule 

 is deeply sunken, smooth, and flat. The ventral margins are finely crenulated. 



Ihis group of species has generally been referred to the subgenus 

 Ventricola, after Dall's selection of Venus rugosa Gmelin, 1798 {^=V. rigida 

 Dillwyn, 1817, not V. rugosa Linne, 1767), as type species. As shown by 

 Myra Keen, 1954 (Jour. Paleontology, vol. 28, p. 217), there is an earlier 

 type designation for Ventricola Romer, 1867, namely that of Kobelt, 1881. 

 Kobelt selected Venus verrucosa Linne, 1758 which makes Ventricola an 

 absolute synonym of Venus. 



Antigona (Yentricolaria) isocardla (Verrill) Plate 50, figure 2 



Venus isocardia Verrill, 1870, Amer. Jour. Sci., vol. 49, No. 146, p. 221 near La Paz. 

 Cytherea {Ventricola) rigida Dillwyn, Dall, 1902, Proc. U.S. Nat. Museum, vol. 26, 



p. 390. 

 Antigona {^Ventricola) isocardia (Verrill), Hertlein and Strong, 1948, Zoologica, vol. 



33, pt. 4, No. 13, pp. 178, 179, pi. 2, figs. 2, 3. 



Shell large, solid, cordate, convex, rotund, the surface sculptured with 

 strong, coarse, elevated, concentric ridges or lamellae, their crests rounded, 

 flattened, or reflexed. On fully grown specimens, the concentric riblets are 

 spaced about two millimeters apart and separated from each other by a 

 deep, flat interspace; the surface of the interspace is often marked with 

 three to six, strong, concentric cords. Fresh specimens show no radial stri- 

 ation but such may appear on the surface of weathered shells. The lunule 

 is small and deep, its surface marked with coarse, crowded concentrics. The 

 left valve has a flat escutcheon; it is absent from the right valve. Color 

 is usually a creamy white overrun with a faint pattern of zigzag lines and 

 larger blotches of light brown, the beak and interior often flushed with 

 pink. 



Length 82.3 mm., height 78.5 mm., semidiameter 27.4 mm. a right valve. 

 Burica Peninsula, Panama. 



This species is questionably distinct from A. rigida (Dillwyn) from 

 Florida and the West Indies. 



Range — Gulf of California to Ecuador. Panama: Burica Peninsula; 

 Coiba Island (USNM); Gulf of Chiriqui (USNM). Colombia: Gorgona 

 Island (Hertlein and Strong). Ecuador: Manta; Isla la Plata. 



Antigona (Yentricolaria) isocardia magdalenae (Dall) 



Cytherea {Ventricola) magdalenae Dall, 1902, Proc. U. S. Nat. Museum, vol. 26, No. 

 1312, pp. 390, 403, pi. 15, fig. 6 off Magdalena Bay on west shore of Lower 

 California. 



