520 MAZATLAN UNIVALVES 
ean 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 afew 
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 itis 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 large specimen (including spines, 
excluding canal) measures long. 1°24, Zaz. 1°14. The smallest, 
with perfect apex, canal probably broken, measures °78 by °5. 
Hab.—(M. reeurvirostris. Gulf Nicoya; in sandy mud, 9 fm. ; 
Cuming. —Panama, 1 imperfect sp. C. B. Adams.)—Mazat- 
lan; not common; L’pool Col. 
Tablet 2467 contains 3 sp. normal growth.—2468, 1 do. form 
of M. rectirostris, labrum nearly smooth, with Ostree.—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 coste; 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 Gastrochena 
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 central.—2480, 
2 normal and 2 abnormal opercula. 
