TRANSACTIONS OF WAGNER 



TERTIARY FAUNA OF FLORIDA 



3. Concentric interspaces smooth or radially striated, the striation sparse, 

 irregular, or local in situation, or general, but always very fine. 



3. The presence or absence on the disk of zigzag brown blotches or linea- 



. tion. 



4. The greater or less conspicuousness of an obscure radial sulcus near the 



posterior dorsal border. 



5. The presence or absence of the internal marginal purple coloration. 



6. The division of the medial smooth space by concentric sulci into more or 



less numerous riblike flattened ridges, which may be smooth or radi- 

 ally grooved ; white or having the notata coloration ; even and uni- 

 form or more or less bifurcate or inosculated distally, but always 

 flattened, except in the fossil variety antiqua. 



The varieties which may be usefully named are: i, variety notata Say, 

 which, in addition to the usual characters, shows zigzag brown painting, espe- 

 cially over the smooth middle portion of the disk, and is usually destitute of 

 purple coloration within ; 2, variety radiata Dall, in which the disk shows be- 

 tween the concentric lamellae fine, even, radial striation ; 3, variety alba Dall, 

 in which the purple coloration is absent, and there are no brown external mark- 

 ings as in notata; 4, variety cancellata Gabb, a rare form in which the median 

 flattened portion is cut into flattish ribs by the continuation across the shell of 

 some of the concentric sulci, while these are transversely grooved by radial 

 sculpture, as in variety radiata. 



Considering the number of mutable elements in this species and V. campe- 

 chiensis, the number of combinations which might be found by sufficiently 

 extensive collecting is obviously very great. But it seems as if science would 

 not profit particularly by devising names for them all. I may note that most 

 of the mutations occur both recent and fossil and are not confined to a special 

 horizon, though they are perhaps due in most cases to especial conditions of 

 water, salinity, temperature, food, or character of the bottom. While it is 

 impossible to cite characters which will invariably distinguish all the varieties 

 and mutations of V. mercenaria from those of V. campechiensis, nevertheless 

 in general they are separable by sufficiently obvious features which apply to 

 both the Miocene fossils, the recent shells, and their intermediate representa- 

 tives. 



I have found the most remarkable mutations in the specimens from the 

 Pleistocene, which may perhaps be due to the changes initiated by the fluctua- 

 tions of temperature and salinity connected with glaciation. 



In specimens from Heislerville, New Jersey, I find some with strong con- 



