206 AXEL A. OLSSON 



Strong concentric riblets which over the anterior slope are partly divided 

 so as to form elongated, concentric nodes. 



Length 9.2 mm., height 8.3 mm., semidiameter 3,6 mm. a left valve. 

 Holotype, ANSP 218936 



Easily recognized by its shape. At present known only from the type 

 specimen, a left valve. 



Range — Ecuador. Ecuador: Santa Elena. 



Family LUCOIDAE 



Shells small or large, subcircular to suborbicular, generally equivalve 

 but occasionally somewhat inequivalve (Miltha), thin or heavy, in the 

 latter case, the interior may be coarsely pustulose. Hinge when typical has 

 two strong cardinal teeth and an anterior and posterior lateral tooth or 

 its socket in each valve, the posterior lateral element placed distantly at 

 the end of the ligamental scar; in other forms, the hinge may be degenerate 

 to a greater or lesser degree, the cardinal teeth and sometimes the laterals 

 become obsolete and often wholly lacking in the adult. The ligament is 

 external, attached to a deeply immersed scar lying below the margin of 

 the valve. Adductor scars ot unequal size, the anterior scar typically much 

 larger, divided, the lower segment narrow and elongated and free from the 

 pallial line. The pallial line itself entire and placed near the margin. Ventral 

 margin smooth or crenulated. Surface sculpture formed by radial or con- 

 centric elements or a combination of both. Often with a scaly periostracum. 



Although the family Lucinidae is well characterized, the definition of 

 smaller taxon units such as genera is more difficult. The Lucinidae have a 

 long geological history and a world-wide distribution especially in the 

 warmer seas; they are, however, poorly represented in the Panamic-Pacific 

 faunal area; some of its species are rare and known only from deep water. 



Key to the genera of the Lucinidae 

 L Hinge teeth present (at least in the young), sometimes becoming 

 obsolete in the adult. 



A. Dorsal areas are well defined on both the anterior and posterior slopes, 

 depressed, set off by a line or groove, or by a marked change of 

 sculpture. 



1. Hinge provided with both cardinal and lateral teeth, one or the other 

 sometimes becomes obsolete. 



Genus LuciruO' 



2. Hinge with cardinal teeth only; no lateral teeth at any stage. 



Genus Miltha 



B. No dorsal areas; the surface marked with radial, cancellate, or a 

 divaricate pattern of sculpture. 



3. Sculpture formed by a series of deeply incised lines in parallel curves 

 and sharply divaricated along the anterior-umbonal slope. 



Genus Divaricella 



4. Sculpture mostly radial, formed of simple, noded or cancellated ribs. 

 Color white, often yellow in the interior, the marginal band sometimes 

 coral red or purple. 



Genus Codakta 



n. Hinge teeth absent (or nearly so) at all stages. 



5. Shell usually round and plump, concentrically sculptured. 



Genus Anodontia 



