214 AXEL A. OLSSON 



Lncina (Parrlluclna) approxlmata (Dall) Plate 31, figure 7 



Phacoides (Parvilucina) approximata Dall, 1901, Proc U. S. Nat. Museum, vol. 23, No. 



1237, pp. 813, 828, pi. 39, fig. 4. 

 Parvilucina tenuisculpta approximata (Dall), Maxwell Smith, 1944, Panamic Marin-e 



Shells, p. 57, fig. 722. 

 Lucina (Parvilucina) approximata (Dall), Hertlein and Strong, 1946, Zoologica, vol. 



31, pt. 3, No. 8, pp. 115, 116. 



Shell small, rounded, nearly equilateral, the beaks high and full, curved 

 over a deeply impressed, lanceolate lunule. The sculpture is produced by 

 small, simple, rounded riblets between narrow interspaces, both neatly 

 cancellated by concentric threads; the radials are strongest on the ventral 

 side of the disk but in some southern shells, they are replaced almost com- 

 pletely by close-set, raised, concentric threads on the umbonal portion. 

 The posterior-dorsal area is flattened to excavated, sculptured by concen- 

 trics only which may enlarge to form two rows of scabrous threads. Size 

 4 to 7 mm. 



Length 6.3 mm. height 6:5 mm., diameter 4 mm. Gulf of California. 

 USNM. 



Range — Monterey California to Panama. 



Lucina (Parvilncina) mazatlanica Carpenter Plate 31, figures 3-3b, 9, 9a 



Lucina mazatlanica Carpenter, 1855, Cat. Mazatlan Shells, Brit. Mus., p. 99, No. 144. 

 Phacoides (Here) mazatlanicus Carpenter, Dall, 1901, Proc. U. S. Nat. Museum, p. 



811, vol. 23, No. 1237. 

 Lucina (Parvilucina) mazatlanica Carpenter, Hertlein and Strong, 1946, Zoologica, vol. 



31, pt. 3, p. 116. 



Shell small, obliquely subcircular, and moderately convex. Anterior- 

 dorsal area having the shape of a large, concave, lunular depression cutting 

 deeply into the margin, the posterior-dorsal area longer, depressed, especially 

 in the smaller shells. Surface principally sculptured with close-set concentric 

 threads, the radials if present small and appear only near the ventral mar- 

 gin. Hinge teeth strong, the ventral margin crenulate. 



Length 3.9 mm.; height 3.7 mm.; diameter 2 mm. Puerto Callo, Ecuador. 



Identification of this small species is based on Carpenter's unpublished 

 drawings in the U. S. National Museum. All the specimens seen are small, 

 (less than 4 mm. in length). 



Range — Gulf of California to Ecuador. Mexico: Mazatlan, Santa Inez 

 Bay. Ecuador: Puerto Callo. 



Genus MILTHA H. and A. Adams, 1857 



Type species by monotypy, Lucina childreni Gray. 



Shell subelliptical to subovate, higher than long, inequivalve, with one 

 valve larger and more convex than the other. Posterior-dorsal area larger 

 than the other and defined by a sharp line or groove. Lunule asyrnetrical, 

 larger in one valve, its margin overlapping the other and lying against the 

 anterior cardinal tooth. Ligament scars deep, the left valve provided with 

 a strong nymphal ridge. Cardinal teeth two in each valve, without laterals. 

 Surface sculptured with fine, threadlike concentrics and weak, vermiculate 

 radial striae. 



