TRANSACTIONS OF WAGNER 

 762 



TERTIARY FAUNA OF FLORIDA 



the same as that of Lamarck. The latter, and not P. plicata, must therefore 

 be cited as the type of the genus. The original specific name must, of course, 

 be retained. 



The genus is easily separated from the Spondyli by the character of its 

 hinge. It may attach itself by either valve ; there is no regularity in this 

 respect within the species. An important memoir by Dcslongchamps on 

 this group is to be found in the Trans. Soc. Linn, de Normandie, ii., 1860. 



Plicatula arose in the Trias and reached its maximum in the later Mesozoic. 

 It is doubtless an offshoot from the Pcctinidce, with which the characters of the 

 hinge, the occasional auriculation, and the presence in some species of internal 

 lirae, appear to connect it. 



Plicatula fllamentosa Conrad. 



PKcatula. filamentosa Conrad, Fos. Tert. Form., p. 38, 1833. 

 Plicatula Mantilli Lea, Contr. Geol., pp. 89, 90, pi. 3, fig. 68, 1833. 

 Plicatula planata Aldrich, Journ. Nat. Hist. Soc. Cin., ix., p. 45, pi. ii., fig. 20, 1866. 



(Young shell.) 

 Spondylus amussiopst- Gregorio, Claib. Mon.,p. 179, pi. 20, figs. 11-13, 1890. (Young shell.) 



Eocene of the Chickasawan or Lignitic at Hachetigbee, and of the Clai- 

 borne sands at Claiborne, Alabama, also at Newton and Wahtubbee, Missis- 

 sippi, and in corresponding beds in Louisiana, Burns, Johnson, Aldrich, Harris, 

 and others ; and in Lee County, Texas, Singley. 



This species is peculiar in its characters. When young it has fine radial 

 striation on both valves, which may sometimes be wholly or partly spiny 

 (mut. planata), and the shell is flattish ; this sculpture changes rather suddenly 

 by an appearance of the large plications, of which the lateral ones rarely bear 

 a few coarse spines. The radial striation continues through life in well-de- 

 veloped specimens, and may be recognized in unworn shells. There are 

 sometimes well-marked auricles developed near the beaks. The interior of 

 the young, as noted by Gregorio, presents a few strong lira; resembling those 

 of Propcamusium ; these persist until middle age, especially distally, but on 

 the disk are gradually buried in shelly matter. The thickened ends of the 

 lira; are visible longer, but gradually disappear, their position in the adult 

 being marked by small pits. 



Plicatula fllamentosa var. concentrica. 

 Wahtubbee Mills, Clarke County, Mississippi ; Burns. 



