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 '085 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. I', lat.'SG, alt. '26. 



A broad sp, '53, '34, '15. 



A conical sp. '58, *4, '23. 



An inaequilateral sp, measures long. ant. '24, long. post. '54. 

 A subsequilateral sp. '23, ,, '29. 



Div. 100 135. 

 Hob. Guacomayo & Gallapagos Is. : under stones on the 



shore ; Cuming. (F. pica) St. Elena and Gallapagos Is. ; 



on dead shells 68 fm. ; Cuming. Yar. Monte Christi, 



Cuming. Mazatlan ; not common ; L'pool Col. 



Tablet 1071 contains the very young sp. 1072, 4 sp. normal 

 shape, different ages. 1073, 5 sp. shewing changes of colour 

 within. 1074, 7 sp. shewing change in form from G. insequalis 

 to G. pica. 1075, 4 sp. shewing change in form of internal 

 callus. 1076, 2 sp. strongly cancellated. 1077, 3 sp. shewing 

 changes from depressed to conical. 



280. GLYPHIS ALTA, C. B. Ad. 



Fissurella alta, C. B. Ad. Pan. Shells, pp. 236, 320, no. 355. 

 Lucapina alta, H. fy A. Ad. G-en. i. 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 Kinmloid 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 Haliotidse. 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. Long. '49, lat. '32, 

 alt. '23, 



