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887 



TERTIARY FAUNA OF FLORIDA 



pclhicida was identified as frftgilis by Gray, most of those who have used 

 the name Standclla have applied it to shells resembling M. fragilis Gmelin, 

 better known as M. brasiliana Lamarck. The ligament in Standclla is Spisu- 

 loid while in M. (Afnctrototna) fragilis it is distinctly Mactroid. The true 

 Standclla was called Spissula'\sy Morch, but it is not Spisula of Gray. The 

 species have much the same distribution in the old world as Lutraria. None 

 is known from North America, but a west African species is found on the 

 coast of southern Brazil. The genus is found in the French Miocene (Helve- 

 tien of Pontlevoy). 



Subgenus EASTONIA Gray, 1853. 

 Type Miiclra ritgosa Gmelin. 



This form is like Slandella, but has the surface radiately striate. The 

 type has the shell less compressed ; the left cardinal narrow, compressed, with 

 a very small, thin accessory posterior lamella (usually lost), and the anterior 

 lateral well separated from the cardinal. Other characters as in Standella. 



Eastonia nicobarica Gmelin (agyptiaca Reeve non Chemnitz) has a hinge 

 like Standella pcllncida. E. Stimpsoni Ball, a species with finer sculpture, 

 from the China Seas, has the hinge similar, but depauperate. This group is 

 iMtricola Blainville, ex parte, 1825, and Merope H. and A. Adams, 1856. The 

 distribution of Eastonia is confined to the warmer seas of the old world. 



Genus HETEROCARDIA -Deshayes, 1854. 

 Type //. i/>/>i>sit/ti (Desh.) H. and A. Adams, Gen. Rec. Moll., ii., p. 387, 1856. 



Shell subequilateral, short, with an arched posterior dorsal slope, and 

 finely vermiculate surface concentrically striated ; hinge-plate produced be- 

 hind and excavated ; pallial sinus deep ; ligament short, external, set off by 

 a shelly lamina; chondrophore moderate, rooljed at the apex; left cardinal 

 wide, small, its posterior arm walling the pit, the anterior arm short, inclined 

 dorsally, crossing the root of a short, high anterior lateral ; posterior laterals 

 short, strong, as in Standclla ; right cardinal wide, posterior arm walling the 

 pit, and the anterior appressed to the dorsal hinge-margin over a buttress 

 roofing the anterior sinus; anterior dorsal lamina short, small; the ventral 

 high and spur-like ; the posterior laminae longer, subequal, rather short. 



This genus bears to Standclla the relation which Jfaclra bears to Spisula; 

 and is especially characterized by its very short, high anterior ventral lamina, 

 and the manner in which the anterior arms of the cardinals arc inclined 

 towards the dorsal shell-margin. The long, excavated backward extension 



