40 . BuivLETIN 9 233 



this young state made by O. compressirostra and O. crenuliniar- 

 ginata, though in these there is generally at least some trace of 

 ribbing, and the muscular scar is heart-shaped as in the adults, 

 PI. 6, fig's 3, 4, represent what we regard as the j^oung of this 

 species. PI. 6, fig. i, is a young O. compressirostra. That these 

 are not Gabb's Gryphcza thirsce is evident from the marked differ- 

 ences shown in thickness, obliquity, form of muscular scars, and 

 above all by differences in direction of lines of growth. 



Localities. — Alabama : Woods Bluff; three miles southwest of 

 Thomasville; near the mouth of Bashi creek. It 

 may be expected wherever Woods Bluff beds crop 

 out. 



Ostrea thirsae, Pl. 6, figs. 5, 6. 



Syn. O. emai'ginata Tuotney, (name only) 2d Biennial Rep't Geol. of 



Ala., 1S58, p. 269. 

 Gryphcea thirsce Gabb, Proc. Acad. Nat. Sci. Phila., 1861, p. 329. 

 Ostrea thirsce Heilprin, 3d Ann'l Rep't U. S. Geol. Surv., p. 311, 



pl. 63, fig's 4, 5, 6. 

 Gryplicea thirsce Aldrich, Bull, i, Geol. Surv. Ala., p. 58, 1886. 



Gabb's origi7ial description. — "Rounded sub-trinangular. Lower 

 valve; beak very small, and close to the hinge, nerver exsert Um- 

 bone rounded, very prominent and somewhat compressed later- 

 ally, the rounded elevation continuing more or less regularly, 

 becoming broader, to the middle of the basal margin, at which 

 point this margin is always somewhat emarginate. Ligament area 

 broad, triangular, transversely striate, and with a slight irregular 

 depression in the middle. Interior of valve very deep. Muscu- 

 lar impression nearly ovoid, narrowest on the inner end. External 

 surface marked by a few small, irregular squamose ridges, most 

 numerous and distin(5l diredtly behind the emargination of the 

 base. Upper valve unknown. 



" The species resembles, remotely, some of the narrower forms 

 of G. vesicutaj'-is Lam.., but after comparing the series before me 

 with numerous authentic specimens of that species, both Ameri- 

 can and European, some of the latter labelled by d'Orbigny and 

 others, b}^ Charlesworth, I am satisfied that they are distin(5l. 

 The beak is so small as to be almost obsolete, and there is always 

 a more or less distin(5l, rounded, umbonal ridge. In general form, 

 it resembles G. {Exogyra) colicmba, but wants the spiral beak, and 

 is never lobed. The small beak and absence of all traces of lobes 



