MAZATLAN UNIVALVES 331 



and changing to another. The adolescent portion is generally- 

 swollen, of smoother growth ; the adult with tho whirls irregu- 

 lar, more or less drawn out, and frequently with sharp ridges 

 of growth behind the labrum. But whatever condition tho 

 adult may assume, the young shell always has one sharp spiral 

 keel in the middle of each whirl, surrounded by spiral strise. 

 The operculum is of uniform colour, with about 18 whirls ; 

 with one row of sharp tubercular hairs next the suture, and 

 other more stumpy ones following ; with a very fine border, 

 radiately striated, followed by a long hairy fringe. The 

 youngest sp. has five whirls, of which the first two are smooth. 

 It measures '048 by "028. An adolescent specimen (12 whirls) 

 measures long. 2 '07, long, spir, 1*64, lot. '74, div. 22. 



The largest (17 whirls) 4'5, 3 '88, '98, 10. 



A slender sp. (15 whirls) 3 7, 3 '2, '82, 8. 



Hob. Acapulco, Humboldt fy Bonpland. Panama, Kiener. 



Payta, Salango, Guacomayo ; in sandy mud, 5 10 fm. ; 



Cumin ff. S. W. Mexico, P. P. C. Mazatlan ; not uncom- 

 mon ; IS pool Col. 



Tablet 1552 contains 6 sp. extremely young. 1553, 2 sp. 

 young ; one passing from chalcedony to purple brown, then 

 suddenly to nearly white, then gradually to dark, linear 

 pattern. 



(1.) Tablet 1554 contains 2 sp. uniform purple black ; one, 

 whirls flat, the other rounded. 1555, 2, sp. very dark, tinted 

 with orange brown. 1556, 2 sp. black purple ground, slightly 

 variegated with white. 1557, 3 do. normal state, with more 

 white ; one has passed through acid, to display colour. 1558, 

 3 do. purple, light abounding ; one in dashes above, clouded 

 below ; another with both large and small pattern. 1559, 3 do. 

 light predominating ; brownish purple in clouds, dashes or 

 spots. 



(2.) Tablet 1560 contains 3 sp. dark olive brown, with purple, 

 linear pattern or variegated. 1561, 2 do. white abounding. 

 1562, 3 do. light tint, linear markings conspicuous. 



(3.) Tablet 1563 contains 1 sp. purple brown passing into 

 orange brown. 1564, 2 sp. nearly uniform orange brown ; one 

 nearly smooth, with blunt shoulder keel; the other rough, 

 keeled above and below. 1565, 3 do. with faint purple brown 

 cloudings; one very slender, lower whirls separating. 1566, 

 2 do. lower whirls passing into normal colouring. 1567, 2 do, 

 upper half of the whirls richly variegated. 1568, 3 do. light 

 predominating ; pattern clouded or dotted. 



