PANAMIC-PACIFIC PELECYPODA 215 



Miltha differs from Lucina in the complete absence of lateral teeth. 

 The type species (Miltha childreni) is a rare shell from the coast of Brazil, 



Miltlia xanthusi (Dall) Plate 30, figure 4 



Phacoides {Miltha) childreni Gray, Dall, 1901, Proc. U. S. Nat. Museum, vol. 23, No. 



1237, p. 812. (Not of Gray, 1825.) 

 Phacoides (Miltha) xanthusi Dall, 1905, Nautilus, vol. 18, No. 10, p. Ill "Cape St. Lucas" 

 Lucina (Miltha) xanthusi (Dall), Grant and Gale, 1931, Mem. San Diego Soc. Nat 



Hist., vol. 1, pp. 291, 292, pi. 14, figs. 20a, 20b.— Hertlein and Strong, 1946, 



Zoologica, vol. 31, pt. 3, p. 115 pi. 1, fig. 13. 

 Phacoides xanthusi (Dall), Pilsbry and Lowe, 1933, Proc. Acad. Nat. Sci. Philadelphia, 



vol. 84, p. 137. 

 Miltha xanthusi (Dall), 1950, Mem. Geol. Soc. America, No. 43, p. 77, pi. 19, figs. 3, 8, 



Shell large, ovately rounded, produced ventrally, rather flat, right valve 

 more convex than the left; ornamentation consists of concentric lines of 

 growth and radial striae; posterior sulcus present, ornamented by one radial 

 ridge; lunule chiefly in the right valve, depressed; two cardinal teeth, the 

 right anterior and left posterior tooth bifid; ligamental groove long, pos- 

 terior; muscle scars, especially the anterior one, large; inner surface of valve 

 scatteringly pitted; margin smooth. (Hertlein and Strong, 1946.) 

 Dimensions. Height 71 mm., width 65 mm. (Dall, 1905) 

 Height 71.2 mm., width 68 mm. (Hertlein and Strong, 1946). 



According to Dall, this Pacific Miltha is closely similar to M. childreni 

 (Gray) from the Atlantic but appears to differ by its smaller adult size, 

 more rounded and more equal valves as well as having a shorter ligament. 

 Whether these characters will prove constant when a larger series of both 

 forms become available for study remains to be seen. According to Hertlein 

 and Strong, young specimens of M. xanthusi have a rounder form. M. 

 joanms (Dall), 1905, incompletely described and unfigured from the Pli- 

 ocene of Lower California, seems to be a doubtful species. It is said to be 

 smaller, heavier, and more rounded. M. caloosaensis (Dall), common in the 

 Pliocene of Florida, is similar to M. xanthusi in general characters; it often 

 reaches a much larger size; the interior becomes much thickened in the 

 adult and the adductor scars deeply inset; its left valve is generally the 

 more convex, the reverse of the condition found in M. xanthusi. M. xanthusi 

 has been recorded as a Pleistocene fossil in Lower California. 



Range — Lower California. 



' Genus CODAKIA Scopoli, 1777 



Type species by tautonymy and monotypy, Chania codak Adanson 

 (=Codakia orbicularis Linne). Recent, Florida, West Indies, and West 

 Africa. 



Shell large or small, suborbicular, equivalve, and moderately convex 

 to depressed. Surface sculptured principally by radial riblets, noded or 

 cancellated by the concentrics. Dorsal areas absent or weakly indicated 

 by a change of sculpture. Lunule small and deeply sunken, confined to 

 the right valve, its margin sharp and fitting into a narrow furrow in the 



