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TERTIARY FAUNA OF FLORIDA 



dividing the area lengthwise into nearly equal parts ; there are traces of very 

 minute radial striation on some specimens ; resilium shorter than the ligament, 

 both deeply inset and partly covered by the dorsal margin, which is usually 

 broken away ; teeth and scars normal, well developed ; disk internally with a 

 well-marked oblique sulcus. Alt. 53.0 (to 63.0), Ion. 47.0, diam. 13.5 mm. 



The lunule is better developed in the older specimens and more in the right 

 than in the left valve. Some specimens have the right valve less convex than 

 the left. The species is very like P. (Milt ha) Childreni Gray, but is propor- 

 tionally more elevated, with a more delicate hinge and smaller muscular im- 

 pressions.- In the Pacific species, when there is a perceptible difiference in the 

 convexity of the valves, it is the left one which is flatter, and it is a curious 

 coincidence that similar differences occur between the Atlantic and Pacific 

 species of Tellidora, also inequivalve shells. 



Phacoides (Miltha) Childreni Gray. 



Tellina Childreni Gray, Ann. Phil., xxv., p. 136, 1824; Zool. Journ., i., p. 221, 1825. 

 Lucina Childreni Gray, Sowerby, Gen. Shells, No. 27, Lucina, fig. 3, 1826 ; Reeve, Conch. 



Icon., vi., LticinOj pi. iii., fig. 12, 1850. 

 Miltha Childreni H. and A. Adams, Gen. Rec. Moll., ii., p. 468, 1857. 



Pliocene of San Juan, Gulf of California, Orcutt ; living in the Gulf of Cali- 

 fornia. 



This is the type of the subgenus and one of the two known living species, 

 the other being a native of Mozambique. 



Phacoides (Miltha) disciformis Heilprin. 

 Lucina disciformis Heilprin, Trans. Wagner Inst., i., pp. 94, 103, pi. xii., fig. 28, 1886. 



Pliocene of the Caloosahatchie and Shell Creek, Florida ; Willcox and Dall. 



This is one of the species of group A, with strong concentric lamellation, 

 recalling Lucinoma; it is close to P. hillsboroensis Heilprin, of the Oligocene, 

 but has longer and less marked dorsal areas and grows to a larger size. Besides 

 their superficial characters the shells of this group are notable for the deep 

 bifurcation of the major cardinal tooth, which appears like two separate teeth, 

 and for the small size of the posterior and extreme narrowness of the anterior 

 adductor scars. The lunule is small, narrow, deep, and somewhat ill-defined. 

 The internal punctation of the disk is often coarse and strong. 



A curious species described by Gabb from the Cretaceous of California 

 under the name of Dosinia (later Lucina) gyrata (Pal. Cal., i., p. 168, pi. xxiii., 

 fig. 148, 1865) is probably a species of Miltha. 1 



