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823 



TERTIARY FAUNA OF FLORIDA 



by sharp, narrow, arcuate grooves in such a way as to produce the effect of a 

 parting on the periphery of the valve. This grooved and faceted sculpture 

 ceases abruptly behind, but the rows of facets are continued as wider longi- 

 tudinal riblets posteriorly. The umbonal reflection is heavy and radially 

 striate; the apophysis seems to have been obsolete and its remains appressed 

 to the internal arch of the umbo. The whole is rather thick and solid, and 

 the antero-posterior length of the fragment is six and a half millimetres. 



The very distinct sculpture of this shell instantly distinguishes it from 

 any other known Teredina. 



The only other Pholads of which I find any mention in our Tertiary liter- 

 ature are P. ovalis Say, which may be a Fistulana, and will be later referred 

 to under that head; and Pliolas petrosa Conrad (Bull. Nat'l Inst., ii., p. 193, 

 pi. 2, fig. 4, 1842 ; and Am. Journ. Sci., 2d Ser., i., p. 213, pi. 2, fig. i, 1846), 

 which is not a Pholad,''' though externally much like one. 



Superfamily MYACEA. 



Family GASTROCH/ENIDyE. 



Genus GASTROCH^NA (vSpengler) Cuvier. 



< Gasfrochma Spengler, Nova Acta Soc. Sci. Hafn., ii., p. 174, 1783 ; Desh., Traite de 



Conchyl., i., p. 26, 1844. 

 •\ Chcena Retzius, Nov. Test. Gen., p. 19, 1788 ; Schum., Essai, p. 94, 181 7. 

 <i Mytilus Brugiiiere, Encyc. Meth., pi. 219, 1792. 

 <[ Fistulana Bosc, Hist. Nat. Coq., ii., p. 208, 1802. 

 Trapezium fi, Megerle, Entw., Neuen Syst. Schal., p. 69, 181 1. 



Gasirochana Cuvier, Regne An., ii., p. 490, 1817 ; Lam., An. s. Vert., v., p. 446, 1818. 

 RoceUaria (Fleuriau IVIS.) Blainv., Diet. Sci. Nat., vol. 57, p. 244, 1828 {G. viodiolina 



Lam.); Tryon, Mon. PholacL, p. 39, 1862. 

 Roxellaria Menke, Syn., p. 121, 1830; Agassiz, Nom. Zool., 1845. 

 GastrochcEiia Fischer, Man. de Conchyl., p. 1128, 1887. 



* Phenacomya n. g. Shell thin, feebly radially sculptured, pholadiform; more or less expanded 

 and truncate anteriorly, adult with a narrow dorsal gape in front of the beaks, shell closed below, 

 equivalve; young with a wide anterior gape which is gradually closed with growth as shown by the 

 incremental lines; shell attenuated and smoother posteriorly. Type Pholadomya ciineata Sowerby, 

 Desh., An. s. Vert. Bassin de Paris, i., p. 277, pi. ix., fig. 6-8, 1868. 



It is very doubtful if the group represented by this type has any very close relation to Phola- 

 domya. 



The American representatives are Pholas pelrosa Conrad, above cited, and Pholadomya Mauryi 

 Harris, Bull. Pal., iv., p. 71, pi. 6, fig. 17 ff, 1896. All are Eocene and, so far as known, the 

 genus is Eocene only. 



