TRANSACTIONS OF WAGNER 



1422 



TERTIARY FAUNA OF FLORIDA 



Cardita planicosta var. angusticardo S. V. Wood, Mon. Eoc. Biv. Engl., part iii., pi. xxi., 

 fig. sc, and expl. of plate, Jan., 1871. Bracklesham, England. 



Cardita planicosta var. laticardo S. V. Wood, op. cit., expl. pi. xxi., fig. sd, 1871. 



Venericardia suessoniensis D'Archiac, Descr. Geol. du dep. de I'Aisne, p. 272, Ade De- 

 shayes ; Mem. Soc. Geol. de France, v., pp. 19s, 272, 193, 1842, Ude Bronn. ^ Cardita 

 planicosta var. minor Deshayes, An. s. Vert. bas. Paris, i., p. 756, 1858 (unfigured). 



In order to get a clear idea of the evolution of the American form it will 

 be in order to take up the various horizons beginning with the lowest Eocene. 

 This will not cover what may be termed the lateral divergencies, or variations 

 of the type in a single horizon, which are often marked. 



Midway Stage. — In the basal Eocene the fossils are badly preserved in an 

 extremely hard matrix, so that it is difficult to be certain of minor characters. 

 However, we have here a small form, less than fifty millimetres in height, 

 which undoubtedly is the precursor of V. planicosta.* This is the V. Mooreana 

 Conrad, Am. Journ. Conch., iii., p. 190, 1867; Harris, Bull. Am. Pal., iv., p. 

 38, pi. iv., fig. 13, 1896. 



Chickasazvan or Lignitic Stage. — In this stage we have developed several 

 well-marked varietal forms. First may be cited the V. ascia of Rogers already 

 referred to from Virginia. Next comes the large, somewhat rostrate, variety, 

 regia Conrad, f from the Eocene of Maryland, Gregg's and Bell's Landings, 

 Alabama. It is usually notable for the depth of the narrow furrows between 

 the ribs, and the Marjdand specimens usuall)' have the concentric striation more 

 intense and irregular than in the typical ascia. Another very marked form is 

 the variety Hornii Gabb, J originally described from California but abundant 

 at Wood's Bluff, Alabama, and especially at Lisbon Bluff in the succeeding 

 stage. It is remarkable in having the furrows linear, the ribs arching over to 

 them, and in the obsolescence of the ribs except on the umbones, where they 

 are sometimes beaded and terraced. The variety laticardo Wood, described 

 from the Bracklesham beds of England, is reproduced at Hatchetigbee Bluff, 

 Alabama. It is the form 8 of Harris (op. cit.). Lastly we have a small, 

 compact form, the V. ascia in miniature, which was described from the lower 

 Claiborne by Conrad as densata, a variety which reaches less than fifty milli- 



* The other forms associated by Professor Harris with this as varieties of V. plani- 

 costa I regard as distinct species ; i.e., Smithii Aldrich, and perantiqua Conrad. 



t Harris, Bull. Am. Pal., ii.. No. 9, p. (55) 247, as form /3, pi. ix., figs. I, 2, 1897. 

 + Harris, op. cit., form 7, p. (55) 247, pi. x., figs. 1-4. 



