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985 



TERTIARY FAUNA OF FLORIDA 



Shell Creek, the Myakka River, etc., south Florida; in the Pleistocene of 

 North Carolina and of North Beach, near Osprey, Florida. Recent from New 

 Bedford, Massachusetts, to St. Thomas, West Indies. Adventitious on the 

 British coast and elsewhere. 



The radial rib always perceptible in normal species, in others is distinct in 

 'the young, but gradually becomes obsolete in the mature shell, showing that 

 Mesopleura is the older type. When the rib is imperceptible the most obvious 

 distinguishing characters of this species are the long nymphs and short pallial 

 sinus. I have seen nothing older than the Pliocene, which seems referable to 

 this species. Emmons' figure is very poor but distinctly different from T. 

 divisus and, if not a young gibbus, may prove to be a distinct species as assumed 

 by Conrad. 



Tagelus {Mesopleura) siibtercs Conrad (1838), from the Pacific coast (not 

 subteres Emmons), is larger than the east coast species and has the same range 

 as T. calif or nianus. The rib is entirely obsolete in the fully matured adults. 

 It is found in the Pleistocene and also living. 



Tagelus lineatus Gabb, 1881, from the Pliocene of Costa Rica, is a Psain- 

 mosolen. There are several species of true Tagelus in the West Indies and 

 southward, which should be compared with any supposed new species which 

 may turn up. 



Family SEMELID^. 



Genus SEMELB Scluimacher. 



Semele Schumacher, Essai, p. 165, 1817. Type Tellina reticulata Spengler, Fischer, Man., 



p. 1 1 S3, 1887, = T. proficua Pult. 

 Amphidesma Lamarck, An. s. Vert., v., p. 489, 1818; Bowdich, Elem. Conch., ii., p. 8. pi. 2. 



fig. 18, 1822. Type A. variegata Lam., = Venus purpurascens Gmelin. 



The Amphidesma of Lamarck was a heterogeneous assembly with no type 

 cited, the first species being A. variegata, which was taken to illustrate the 

 genus by Bowdich four years later. Fortunately Schumacher had proposed 

 Semele a year earlier than Lamarck with a single type, about which there is 

 no uncertainty. The genus makes its appearance in the Eocene and is well 

 represented subsequently up to the present fauna. It differs from Scrobicu- 

 laria, which has a very similar hinge, by the characters of its ctenidia, which 

 are like those of Tellina. The genus is divisible into two sections. 

 Section Semele s. s. Type S. proficua Pulteney. 



Shell large, sculpture radial and concentric or oblique, reticulate, or nearly 

 absent ; chondrophore elongate, resilium large and strong, ligament external, 



