FREE INSTITUTE OF SCIENCE 



TERTIARY FAUNA OF FLORIDA 



Section Miorangia Dall, 1894:, 

 Type Giiatliodon JoJinsoiti Dall. Miocene of Mississippi. 



Shell small, extremely inequilateral ; pallial sinus obsolete ; cardinals 

 reversed from the normal, that in the left valve fitting over the other. 



This a peculiar little form from the newer Miocene of the Gulf border. 

 So far as my observations go, it is the only species in the whole family which 

 presents us with a superior left cardinal. 



Subfamily PTEROPSIDINiE. 

 Genus PTEROPSIS Conrad, i860. 

 Type Liitrarla papyria Conr., 1S33 (= M. dcntaia Lea). 



Shell subequilateral, thin, inflated, with a more or less vermiculate surface; 

 pallial sinus deep, narrow, pointed ; siphonal gape small ; ligament sagittate, 

 not set off by a shelly lamina from the chondrophore ; dental armature strong ; 

 chondrophore large, shallow; left cardinal tooth wide, the anterior arm super- 

 posed on the root of the anterior lateral, the posterior arm walling the pit; 

 posterior lateral long and well marked ; right cardinal wide, the anterior arm 

 walling the pit, the posterior smaller, appressed upon the dorsal shell-margin ; 

 arms of the cardinal coalescent above, spur perceptible, not roofing the pit ; 

 laminae short, smooth, the anterior emerging from the ventral sinus ; hinge- 

 plate very oblique, thin ; dorsal areas obscure. 



This group comes from the Lower Eocene, Lisbon or Buhrstone horizon, 

 and the Claiborne sand, where it is represented by a single species in each 

 horizon. The Claiborne species is the type ; that from the Buhrstone is 

 Lutraria lapidosa Conr. (1846), of which Astarte Coiiradi Dana (1863, Man. 

 Geol., fig. 800) is a synonyme. 



This group is, without doubt, the precursor of Raeta, and should be 

 looked for in the Tertiaries of Eastern Asia. It differs from Rdita in the 

 strong, not concentrated hinge, well-developed laterals, broad, rotated right 

 cardinal, and in having no shelly lamina between the ligament and resilium. 

 It corresponds to Spisiila, as does Raeta to Mactra in the MactrincB. 



Genus LABIOSA (Sclimidt) Moller, 1S32. 

 Type Mactra anatina Spengler, 1802. 



Shell large, thin, inflated, broad and gaping behind, beaks adjacent; sur- 

 face concentrically striate; dorsal areas well defined, the posterior area set off 

 by an elevated line; pallial sinus short, rounded, wide ; siphonal gape wide ; 



