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57' 



TERTIARY FAUNA OF FLORIDA ^ ' " 



Chico of California (A^. truncata Gabb) which is reported by Gabb to extend 

 upward into the Tejon Eocene (Pal. CaL, i., p. 198, pi. 26, fig. 184; ii., p. 197). 



An examination of undoubted Cretaceous specimens of N. truncata 

 shows that the species differs from the Tertiary forms by its more impressed 

 escutcheon, its finer and more delicate divaricate sculpture, and its more 

 prominent close set, regular and even concentric sculpture. Those I have 

 seen are also smaller. They are quite distinct from N. Erinani, which may 

 eventually prove to be of Tertiary age. 



Some confusion has been caused by the too inclusive manner in which 

 Gabb has treated the fossil forms of the Pacific coast. I find a large Eocene 

 species which is not distinguishable from N. decisa Conrad, the latter being 

 a second name for N. divaricata Conrad (1848), not of Valenciennes (1833), 

 nor of Hinds (1843), which was afterwards named N. Coiiradi hy Meek (S. I. 

 Miocene Checklist, p. 27, 1864). This probably extends into the Miocene, 

 and to assist in clearing up the difficulty I have included a figure of it (plate 

 40, figures I, 3). In unmistakable Miocene of Oregon, on the Nehalem 

 River, near Mist, Columbia County, another form is found of smaller size and 

 much coarser sculpture, the posterior end more distinctly rostrate, but other- 

 wise very similar, for which I propose the name of Nitcida [AcUd) cordata 

 (plate 40, figure 4). The interesting point, however, is that none of the fossil 

 forms can be properly united with the recent N. divaricata Val. in spite 

 of Gabb's opinion. The latter is a more trigonal, compact, and less rostrate 

 form, and clearly distinct. The fossil forms are more closely related to the 

 recent species of Japan than to the existing west American shell. Like 

 many other Pacific groups, Acila extended to the Antillean region through 

 the gaps between the Central American archipelago in Oligocene times. It 

 is represented by N. SchoDiburgki Forbes, from the San Fernando beds of 

 Trinidad, which differs from the west American fossils by its more rostrate 

 shell, and by TV. tubercidata Gabb, from the Oligocene of Hayti. It is 

 possible that deep-sea dredgings will eventually reveal a surviving species in 

 the abysses, but to the present time no recent species is known from the 

 Atlantic and only the N. Cobboldice from the Pliocene of the British Crag 

 beds. No east American fossil species is known at all from the continent of 

 North America. The species have, as a rule, twenty to twenty-two anterior 

 and nine to eleven posterior teeth ; the posterior tooth in the left valve nearest 

 the chondrophore is larger than those immediately behind it. All the species 

 have concentric sculpture. 



