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 Gr. alta. A young 

 specimen '083 in length, displays a flattened spiral vertex as in 

 E,imu.la, with the hole adjacent, well- formed and encroaching 

 on the vertex, withoiit channel ; ou.tside suboval, very slightly 

 constricted ; inside with the callus not trimcate. The largest 

 specimen measures long.l', lat.'56, alf.'2Q. 



A broad sp. „ "SS, „ "34, „ "15. 



A conical sp. ,, '58, ,, '4, „ '23. 



An inaecxiiilateral sp. measures lony. ant. "24, long. post. '54. 

 A suba?quilateral sp. „ ,, '23, ,, "29. 



Div. 1000—135". 



Sah. — Guacomayo & Gallapagos Is. : under stones on the 

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

 on dead shells 6—8 fm. ; Cuming. — Var. Monte Christi, 

 Cuming. — Mazatlan ; not common ; Upool 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. 



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

 Lucapina alta, H. Sf A. Ad. Gen. i. 447. 



This prcttj^ little species is known by its very conical, 

 narrowed sliape, and strong canceUating ribs. The smallest 

 specimen '01 in length, displays a well ciuwed 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 Haliotida;. Another specimen, 

 though only "1 in length, has lost all trace of spire, but presents 

 the characteristic suboval, slightly bilobed hole of the species. 

 Tlie shell is produced and thick at the vertex : interior callosity 

 truncate and slightly indented anterioi'ly. Long. "49, lat. 32, 

 alt. -23. 



