286 AXEL A. OLSSON 



6. Shell smaller (length 35 mm. or less), the surface uniformly colored 

 white or violaceous-brown, the dorsal areas similar. 



L. circinata vinaceous 



D. Concentrics higher and much more irregular, the individual lamella 

 varying much in height and in spacing. 



7. Shell subovate in shape, white in color. 



L. callicomata 



Lamelliconcha circinata altemata (Broderip) Plate 48, figures 1-lb 



Cytherea alternata Broderip, 1835, Proc. Zool. Soc. London, p. 45 Monte Christi. 



Cytheraea circinata var. C. alternata Broderip, Sowerby, 1851, Thes. Icon., vol. 2, 

 Cytheraea, p. 631, No. 65, pi. 132, fig. 104 West Colombia, Cuming. 



Dione alternata (Broderip), Reeve, 1863, Conch Icon., vol. 14, Dione, pi. 7, figs. 28a, 

 28b. These figures are stated to be the types of Broderip's alternata and 

 referred by Deshayes to D. circinata. — Romer, 1868, Monogr. Molluskengatung 

 Venus, Linne, bd. 1, 5, Sectio: Dione Gray, pp. 136, 137, pi. 36, fig. 2. 



Pitar {Lamelliconcha) circinatus alternatus (Broderip), Hertlein and Strong, 1948, 

 Zoologica, vol. 33, pt. 4, No. 13, pp. 174, 175. 



Shell trigonal-ovate, convex, the beaks placed at the anterior one-third, 

 curved slightly forward, the posterior-dorsal margin arched, the anterior 

 end well rounded. The lunule is small, cordate, deeply impressed and dark 

 in color, even though the rest of the surface is white; there is no escutcheon, 

 the dorsal margin bordered by a cord only. The surface is marked with 

 strong, narrow concentric ridges of nearly uniform strength over most of 

 the disk but they may show some alternation on the sides. The color of 

 most specimens is white, except the lunule and the posterior-dorsal margins 

 which are stained with chestnut red: some specimens (as many from 

 Manta) have narrow, radial rays or hnes across the umbones. The pallial 

 sinus is large, rounded at the end and extends to about the middle of the 

 shell cavity. 



Length 44.7 mm., height 40.2 mm., diameter 27.4 mm. Santa Elena, 

 Ecuador. 



The Pacific shell described by Broderip as Cytherea alternata cannot 

 consistently be separated from the common, Caribbean form of L. circinuta 

 (PI. 48, fig. 3). In a large series of L. alternata from Manta and other 

 nearby stations in Ecuador, the concentric lamellation of the surface sculp- 

 ture is fairly uniform in size and spacing, only rarely do they show strong 

 alternation. On the other hand, Caribbean shells, such as from the north 

 coast of Panama and Costa Rica, may show the concentric lamellae alter- 

 nating in strength to a marked degree; these Caribbean specimens then 

 resemble fossil forms from the Miocene of the Dominican Republic. 



L. circinata alternata is a common shell along parts of the Ecuadorian 

 coast and occasional specimens may grow quite large (length S6 mm.), 

 larger than any L. circinata circinata seen from the Caribbean. Most shells 

 are white except for the lunule and posterior-dorsal submargins which are 

 chestnut-brown. They may also show a series of small, red rays over the 

 umbones as illustrated by Sowerby in the Thesaurus. 



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

 Guanico. Colombia: Isla del Gallo. Ecuador: Manta; Sua; Santa Elena. 

 Peru: Mancora. 



