TRANSACTIONS OF WAGNER 

 802 



TERTIARY FAUNA OF FLORIDA 



Stalagiiiiiini Conrad, Fos. Tcrt. Form., p. 39, Oct., 1833. Type S. margaritacettm 



Conrad, /. c. 

 Hippagns Lea, Contr. Geol., p. 72, Dec., 1833. Type N. isocardioides Lea, /. c., pi. 2, 



fig. 50. 



Myoparo Lea, Contr. Geol., p. 73, Dec., 1833. Type J/. costatiis Lea, /. c., pi. 2, fig. 51. 

 Nuculocardia Orbigny, Moll. Cubana, ii., p. 310, 1847 (Spanish edition and atlas, 1845). 



Type N. divaricata Orb., /. c., p. 311, pi. xxvii., figs. 5659. 

 Crenellodon Edwards, MS. Syst. List., Edw. Coll. B. M., p. 14, 1891. Type Crcndla 



pulchcrriina Edw., MS. Oligocene, Brit. 

 Not Crcndla Sowerby, Conch. Man., p. 297, fig. 136, 1842. 



This interesting little group extends through the Tertiary and, owing to 

 the little study given to its characters, has received many names. The shell 

 is usually convex and ovoid, with more or less incurved beaks, a nacreous 

 inner layer, thin epidermis which adheres closely to the shell, and a fine radial, 

 often crossed by a concentric, striation. In young shells the provinculum is 

 exceptionally well developed, sometimes recalling the hinge of Niictila by its 

 strong and projecting denticulations. If the shell is thin, these become obso- 

 lete with growth, but in some species are replaced by a series of denticulations 

 directly consequent on the impingement of the external sculpture on the car- 

 dinal margin, thus repeating a second time in the same individual the process 

 by which the provinculum was originally initiated in its ancestors. At least 

 that is the way in which the writer interprets the facts. When the shell is 

 thick, or when the external sculpture is very delicate, no secondary denticula- 

 tions appear in the adult, which is then left with a practically unarmed hinge- 

 line. The appearance of the provinculum is not dependent on the existence of 

 external sculpture, but the secondary denticulations are so dependent. The 

 exterior may be almost perfectly smooth and polished with only microscopic 

 striation ; finely radially striate without decussation (like C. scriccii), decussate, 

 or with the radial sculpture strong and divaricate. Usually the sculpture is 

 uniformly distributed over the surface, but occasionally there will be an area of 

 unstriated separating two of striated surface, as in Modiolaria, but without the 

 impressed boundaries of the latter genus. 



The form of the foot and the short siphons separate Crcnella generically 

 from Modiolaria, as far as yet shown, but the modifications of the surface upon 

 which the former has been divided into genera are, in the writer's opinion, of 

 little more than specific value. Hippagus is a thick shell with feeble sculpture, 

 and therefore the provinculum is not succeeded by a series of secondary den- 

 ticulations. Otherwise it is an ordinary rather obese Crenella. Stalagmium 



