FREE INSTITUTE OF SCIENCE 



TERTIARY FAUNA OF FLORIDA 



is therefore not entitled to be cited for earlier work in synonymy. However, 

 if he were, the name Trigonella, which he applied to the Mactras, was preoc- 

 cupied by other authors. 



Subgenus CCELOMACTRA Dall, 1895. 



Type M. vio/acca (Ch.) Gmelin. 



Shell equilaterally oval, thin, inflated, with a thin lineated epidermis ; 

 dorsal areas grooved ; beaks adjacent ; pallial sinus very short, high, rounded 

 behind; valves nearly close-fitting, convex; ligament sagittate, linear, com- 

 pletely shut off from the chondrophore by shelly matter; dental armature not 

 concentrated ; laterals long, thin, and flexuous, distally confluent with the 

 hinge-plate margin, as is the anterior ventral lamina; anterior sinus roofed by 

 a buttress upon which stands the anterior arm of each cardinal, and from 

 under which the laterals emerge; chondrophore roofed at the apex; right 

 cardinal not coalescent above, the anterior arm adjacent to the dorsal shell- 

 margin; hinge-plate very oblique, especially in front, forming a deep recess 

 extending to the beaks. 



This group, recognized, but not named, by Gray in 1837 {Mactra D), is the 

 analogue in the Mactra line of ScJiizodesnia in the Spisula line, from which 

 it differs in its ligament, set off by a shelly floor, in its short, high, almost 

 obsolete pallial sinus, the light, inflated valves, the remarkable anterior sinuses, 

 and the disposition of the cardinal teeth. Mactra turgida Gmelin {tiimida 

 [Ch.] Rve.), and probably M. Cmningii Reeve {= Cuvieri Desh.), have similar 

 features. It is a tropical old-world group of species. 



Subgenus MACTRODERMA Dall. 



Mactrodo-ma Dall, Nautilus, viii., p. 39, 1894. Type M. velala Phil. 



Shell inequilateral, rude, with a coarse epidermis, pronounced pedal gape, 

 a lanceolate sunken ligament, an inconspicuous spur ; 'dental armature con- 

 centrated, teeth and lamina; short, the anterior arm of the right cardinal lying 

 in the plane of the ventral lamina ; otherwise as in Mactra. 



Section Mactrodcrma s. s. 

 Shell elongated. Distribution, west America. Mactra velata Phil., 

 Panama. 



Section Cyclomactra Dall, 1895. 



Shell subcircular, compressed, pedal gape obsolete, ligament submerged 

 except the tip, but wholly separated from the resilium ; remainder of char- 



