PANAMIC-PACIFIC PELECYPODA 207 



Genus LUCINA Brugui^re 1797 

 {Phacoides Blainville, 1825 and Phacoides "Blainville" Gray, 1847.) 



Type species by subsequent designation, Anton, 1838, Lucina pensyl^ 

 vanica Lamarck {Vemis pensylvanica Linne). Recent, Florida, and the 

 West Indies. 



Shell rounded, thin or solid, more or less convex, the dorsal areas 

 usually well defined, depressed or flattened, or set apart by a change of 

 sculpture. Surface sculptured with strong concentric or radial riblets, 

 sometimes with both. Lunule if present small, sunken; no escutcheon. Hinge 

 teeth well developed or partly degenerate. Ventral margin plain or crenu- 

 lated. 



Typical Lucina is not known from the Panamic area. It has deeply 

 excavated dorsal areas, strong hinge, and heavy concentric sculpture. Most 

 of the minor groups, herein considered as subgenera of Lucina, were placed 

 in Phacoides by Dall. 



Key to the Subgenera of Lucina 



I. Sui-face of shell sculptured with concentrics only. In Lucina, s.s., the 

 concentric edges of the periostracum is cut into by radial, riblike scales. 



A. Hinge strong, the cardinal and lateral teeth both well developed. 



a. Dorsal areas strong, set apart by deep grooves. 



1. Lunule small or wholly absent. 



Lucina, s.s. 



2. Lunule large and deep. 



Here 



b. Dorsal areas poorly developed or absent. 



3. Shell small, the valve margins deeply crenulated. 



Cavilinga 



B. Hinge structure weaker, either the cardinal or lateral teeth becoming 

 obsolete. 



c. Lateral teeth persisting, the cardinal teeth small or become obsolete 

 as the shell attains maturity. 



4. Shell of medium or large size, lentiform, the dorsal area deeply im- 

 pressed. Sculpture concentrically lamellose. 



Phacoides 



d. Cardinal teeth persistent, the laterals become obsolete. 



5. Subequivalve, lentiform, the surface sculptured with widely spaced, 

 concentric lamellae, their interspaces striated. Mainly in deep water. 



Lucinoma 

 II. Surface sculptured with both radial and concentric elements. 



C. Dorsal areas well developed. 



6. Surface radial ribs large and few in number. 



Pleurolucina 



e. Radial and concentric elements in the sculpture of nearly equal size. 



7. Like Codakia in shape and surface sculpturing but with well-defined 

 dorsal areas. The cancellate sculpture often sharply nodose or beaded. 



Lucinisca 



8. Shells usually small, with coarsely cancellated sculpture, the radials 

 often large and riblike. 



Bellucina 



