MAZATLAN UNIVALVES 221 
so that no point can be fixed on where one begins and the 
other ends. The present series is carefully selected from 
several hundred specimens, with a view to shew the gradations 
and extremes of variation. The external surface is more or 
less strongly cancellated, and the margin similarly denticulated. 
Very rarely it approaches the form of G. alta. A young 
specimen ‘O85 in length, displays a flattened spiral vertex as in 
Rimula, with the hole adjacent, well-formed and encroaching 
on the vertex, without channel; outside suboval, very slightly 
constricted ; inside with the callus not truncate. The largest 
specimen measures long.1°, tat. °56, alt. “26. 
A broad sp. pats (OOS sae On, eee 
A conical sp. Se EOO sth cen, meee 
An inequilateral sp. measures long. ant. *24, long. post. “54. 
A subequilateral sp. ie me °23, 3 “29. 
Div. 100°—135°, 
Hab.—Guacomayo & Gallapagos Is.: under stones on the 
shore; Cuming—(F. pica) St. Elena and Gallapagos Is. ; 
on dead shells 6—8 fm.; Cuming.— Var. Monte Christi, 
Cuming. —Mazatlan ; not common; L’pool Col. 
Tablet 1071 contains the very young sp.—1072, 4sp. normal 
shape, different ages.—1073, 5 sp. shewing changes of colour 
within.—1074, 7 sp. shewing change in form from G. inequalis 
to G. pica.—1l075, 4 sp. shewing change in form of internal 
callus.—1076, 2 sp. strongly cancellated.—1077, 3 sp. shewing 
changes from depressed to conical. 
280. GuiypHis atta, C. B. Ad. 
Fissurella alta, C. B. Ad. Pan. Shells, pp. 236, 320, no. 355. 
Lucapina alta, H. & A. Ad. Gen. 1. 447, 
This pretty little species is known by its very conical, 
narrowed shape, and strong cancellating ribs. The smallest 
specimen ‘04 in length, displays a well curved Rimuloid apex, 
and a round central hole, without channel; another smaller 
hole in the spire may be accidental, or it may display the 
relationship of the family to Haliotide. Another specimen, 
though only ‘1 in length, has lost all trace of spire, but presents 
the characteristic suboval, slightly bilobed hole of the species. 
The shell is produced and thick at the vertex : interior callosity 
truncate and slightly indented anteriorly. Zong. 49, lat. °32, 
alt. *23. f 
