520 MAZATLAN UNIVALVES 



can have no doubt. The most acuminated form, in which the 

 first whirls scarcely touch, exactly agrees with the figures of 

 M. rectirostris : others are as depressed as M. recurvirostris ; 

 most take the form of M. nigre^cens. In colour they most 

 accord with M. funiculatus, but never approaching the char- 

 acteristic painting of that species. They differ from M. 

 nigrescens and M. recurvirostris in the constant spines on the 

 spire ; from M. messorius (which is probably an analogous 

 Atlantic species ; Senegal, Kiener,) in the straightness of the 

 canal spines. The Mazatlan species is characterized, in all its 

 varieties, by a light bluish slate colour, with orange brown on 

 the spiral ribs ; the last varix always having one short spine 

 above the periphery, none below on the middle, but a few 

 scaly ones on the front side (the back being pitted) and one 

 spine on the canal ; the preceding ones either having the same 

 sculpture, or developing medial short spines, and two (rarely 3) 

 on the canal. There is a tendency to irregular growth in the 

 canal, but it is generally straight with the axis of the shell. 

 Living specimens are scarcely ever incrusted. A normal sp. 

 measures long. 2*06, long. spir. '45, long, canal. 1" lat. 1* 

 div. 80.- An acuminated specimen of the same breadth, has 

 long. spir. '65, div. "65. A laige specimen (including spines, 

 excluding canal) measures long. 1*24, lat. 1'14. The smallest, 

 with perfect apex, canal probably broken, measures '78 by *5. 



Sab. (M. recurvirostris. Gulf JNlcoya ; in sandy mud, 9 fm. ; 

 Cuming. Panama, 1 imperfect sp. C. J3. Adams.) Mazat- 

 lan ; not common ; L'pool Col. 



Tablet 2467 contains 3 sp. normal growth. 2468, 1 do. form 

 of M. rectirostris, labium nearly smooth, with Ostrese. 2469, 



1 do. varices thin. 2470, 2 do. much swollen. 2471, 1 do. 

 spines developed. 2472, 1 do. labial tubercles developed. 

 2473, 5 sp. shewing changes of intervarical costse ; the first, at 

 the end, obsolete ; the second, with one ; the third, with two ; 

 the fourth, with three ; the fifth, behind the penultimate varix, 

 with four, ill developed. 2474, 3 sp. canal twisted. 2475, 1 sp. 

 with egg case. 2476, 1 sp. with repaired fracture. 2477, 2 sp. 

 orange tint developed. 2478, 1 sp. with burrow of Gastrochsena 

 along . the penultimate varix. The creature not having room 

 to construct a siphon gallery, has made a projecting pipe. 

 2479, 1 sp. with operculuni abnormal, nucleus central. 2480, 



2 normal and 2 abnormal opercula. 



