110 CONTRIBUTIONS 
pointed; suture very small; columella much thickened 
above ; outer lip sharp; callus folding into the superior 
part of the umbilicus; umbilicus large; whorls four, 
rather depressed above and rounded below ; mouth ovate, 
being about three fifths the length of the shell. 
Length .5, Breadth .5, of an inch. 
Observations. Somewhat allied to gibbosa, but differs in 
the form of the whorls and the length of the spire. The 
last whorl of the mamma is so large that but a small por- 
tion of the superior whorls is visible. 
The genus Natica is widely spread through the various 
strata from the Inferior Oolite to the Crag in Great Britain, 
where nearly twenty species have been observed. Twelve 
of these have been found in and about the London Clay. 
M. Deshayes mentions forty-one as being found in the 
Tertiary period, being well distributed through the Plio- 
cene, Miocene and Eocene periods. In this country, Dr 
Morton has found casts in the Cretaceous Group of New 
Jersey, and four have been described by Messrs Say and 
Conrad from the Tertiary of Maryland. 
