INSTITUTE OF SCIENCE, PHILADELPHIA. 369 



This species is a rather variable shell, which in part accounts for the 

 numerous synonyms. It extends throughout the Chesapeake Miocene, from 

 Maryland to Florida, passes into the Pliocene and Pleistocene, and extends 

 in the living state from Massachusetts Bay southward to Florida, and west- 

 ward to Vera Cruz, Mexico. 



The species from the Chesapeake Miocene in the National Collection, 

 without exception, belong' to the variety percallosa Conr., which has the 

 umbilicus filled with callus ; the Pliocene specimens I have examined are all 

 typical duplicaia, in which the umbilicus remains partly free from callus. 

 The recent specimens offer both varieties in abundance. I note in the recent 

 shells, of which I have examined a very large number from all parts of the 

 coast, that the tendency, other things being equal, is for the southern speci- 

 mens to have a depressed form and wide umbilicus with a relatively small 

 amount of callus. The variety campeachiensis represents the extreme of this 

 tendency, all gradations being observable in a collection of specimens cover- 

 ing a sufficiently wide geographical range. The usual differences exist be- 

 tween the sexes, the male being smaller, more conical, generally with a 

 proportionately higher spire and darker-colored, though the color also varies 

 with the ground on which they live ; specimens from a clean sand-beach are 

 always lighter-colored, generally less elevated and larger than specimens from 

 a muddy shore. The small, elevated dark males were described by Dr. 

 Gould as N. fossata. A depressed but well-grown female accords with Con- 

 rad's N. Emmonsii ; his A^. densata is an equally well-grown male. Exactly 

 similar mutations exhibit themselves in the Pacific Coast species, N. Rechiziana 

 Desh., which is otherwise very nearly related to N. diiplicata. N. Recliiziaiia 

 extends to the Miocene on the Pacific, and it has been described under several 

 names, such as N. inczana and N. ocoyana Conr., and perhaps N. saxea Conr. 

 and N. callosa Gabb. 



Natica Milleri Gabb, from the figure, might be a Ncverita. It is from the 

 Miocene of Costa Rica. Sigaretus munisnialis Gabb also greatly resembles a 

 small Neverita which has accidentally lost its callus. 



Subgenus Lunatia Gray. 



Lunalia Gray, P. Z. S. 1847, P- i49- Type N. ampullaria Lam. 



Naticina Fischer, Man. Conch., p. 766, 1885, not of Guilding, Trans. Lin. Sec. v. p. 31, 1834. 



Nalica Risso, not of Lamarck. 



In describing his genus Naticina, Guilding describes N. lactea of the West 

 Indies as its type. This species was indicated by Dillwyn under the name of 

 Nerita mammilla var. B, to which Nerita rutida Donovan was wrongly re- 

 ferred as a synonym. Herrmannsen therefore cites Natica nitida Don. as 

 the type of Naticina, supposing Dillwyn's synonymy to be correct. This 

 seems to have misled Dr. Fischer, who knew Donovan's species to be a 

 Limatia, into supposing that the type of Naticina Guilding was a Lunatia, 



