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. nigrescens. 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-OG, long. spir. '45, long, canal. V lat. I' 

 div. SC.^ An acuminated specimen of the same breadth, has 

 long, spir.- 65, div. '65°. Alaige specimen (including spines, 

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

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



Ilab.—{M. rccurvirostris. Gulf Nicoya ; in sandy mud, 9 fm. ; 

 Cumhig.—Vanama, 1 imperfect sp. C. B. Adams.)— 'Ma.za.t- 

 lan ; not common ; L'pool Col. 



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

 of M. rectirostris, labium nearly smooth, with Ostrea?.— 2469, 



1 do. varices thin.— 2170, 2 do. much swollen.— 2471, 1 do. 

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

 2473, 5 sp. shewing changes of intervarical costae ; 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 foiir, ill developed.- 2^174, 3 sp. canal twisted.— 2^175, 1 sp. 

 with egg case.- 2176, 1 sp. with repaired fracture.— 2477, 2 sp. 

 orange tint developed.— 2478, 1 sp. with burrow of Gastrochtena 

 along the penultimate varix. The creature not having room 

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

 2479, 1 sp. with operculum abnormal, nucleus ccutral.— 2480, 



2 normal and 2 abnormal opcrcula. 



