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877 



TERTIARY FAUNA OF FLORIDA 



The type is found in California, and the group is represented in the Oli- 

 gocene of Florida and the Eocene of Trinidad. 



Subgenus MACTRELLA Gray, Jan., 1853. 

 Dall, Nautilus, viii., p. 40, Aug., 1894. Type i\f. alata Spgl. (-)- Papyrina Morch, April, 



'853). 



Shell trigonal, thin, inflated, the posterior dorsal area marked off by a 

 keel or angle; beaks prominent; ligament narrow, sagittate; dental armature 

 concentrated, anterior laterals short. 



Section Mactrclla s. s. 

 PLATE 27, FIGURE 14. 

 Mactrella Uall, Nautilus, viii., p. 40, 1894. 



Chondrophore small, oblique, apical ly roofed ; the pit walled in front by 

 the posterior cardinal arm in the right and by a well-marked accessory 

 lamella in the left valve ; anterior laterals very small and short ; both ventral 

 laminae formed by the upturned edge of the hinge-plate ; cardinal tooth in 

 the left valve rather petaloid, the anterior arm stronger than the other, sup- 

 ported at the angle and at the ventral extremity by a septum extending to 

 the dorsal margin of the valve ; there is a feeble anterior accessory lamella 

 superposed on the root of the anterior lateral lamina and a posterior ditto 

 walling the chondrophore ; in the right valve the arms of the cardinal are 

 not coalescent above ; the anterior arm is supported by a septal buttress at 

 each end, and has a small projection below it on the edge of the hinge-plate, 

 representing an accessory lamella'; the gape is short and wide; the surface 

 of the valves is smooth. 



Section Harvella Gray, 1853. 

 Dall, Nautilus, viii., p. 40, 1894. Type M. clegans Sowerby. 



Hinge like the typical section ; surface of the valves plicate ; shell ex- 

 tremely thin. 



This group includes J\f. ritrca Ch. and M. Rccvcsii Gray. 



Section Mactrinula Gray, 1853. 

 Type M. plicataria Lamarck. 



Shell externally like Harvc/la, the dental armature less concentrated, the 

 chondrophore large and narrow, laterals well-developed, emerging in the 

 right valve anteriorly from a roofed sinus, on the roof of which is set the 

 anterior cardinal arm; in the left valve the posterior cardinal arm projects over 



