MAZATLAN UNIVALVES 495 
Buccinum luteostoma, Azen. Icon. Conch. p. 110, pl. 30, f. 1.— 
Hyd. § Soul. Voy. Bonite, pl. 41, f. 5-7 :—B. M. Cat. p. 25, 
no. 203. 
Nassa xanthostoma, Gray in Zool. Beech. Voy. 1839, p. 127, 
pl. 36, f. 3:—Fig. Moll. An. pl. 85, a, f. 5. 
(Nassa) Phrontis xanthostoma, H. & A. Ad. Gen. 1. 118. 
This abundant shell is sometimes of a nearly uniform brown ; 
sometimes striped with light ; sometimes of a uniform yellow- 
ish brown. The yellow colour of the characteristic broad flat 
jabium varies in intensity, being sometimes very slight. The 
spire varies somewhat in amount of acumination. ‘The oper- 
culum is irregularly triangular, with two rounded sides, sharply 
serrated ; the apex being lateral, and turned against the 
anterior wave in the labrum ; the third side, being convex and ~ 
smooth, against the labial portion. The vertical angle varies, 
and the serrations are more or less close, (sometimes as many 
as 15,) obsolete towards the apex. <A large number of opercula 
were found more or less abnormal; the apex being more or 
less internal, as in Buccinum, with the serrations either absent, 
or very few in number. The muscular scar occupies the 
basal portion. The smallest of the adult specimens mea- 
sures long. 6, long. spir.*2, lat. °43, div. 55°. 
An acuminated sp.,, ‘88, x “Ain ilts, 4 GOO ag OUEe 
Amordinary sp. ,, “875 °  ., "38; 633 02, a mone 
fTab.—Real Llejos and Acapulco, Lesson in Rev. Zool. Aug. 
1842.—[ Senegal, Aiener, Perr.—Australia, Metcalf in B. M. 
err. |—Panama; 330 sp. on sand, usually not far below high 
water mark, in places where water is running during the 
recess of the tide; also in similar places not far above low 
water mark ; C. B. Adams.—Mazatlan ; extremely abun- 
dant; L’pool & Havre Coll. 
Tablet 2366 contains 5 sp. young.—2367, 5 do. lip forming.— 
2368, 5 do. nearly mature.—2369, 5 sp. lip light coloured.— 
2370, 7 do. normal state.—2371, 3 do. lip dark.—2372, 3 sp. 
spire acuminated.—2373, 5 sp. shewing colour of back.—2374, 
5 do. after acid treatment.—2375, 4sp. mended after fracture.— 
2376, 3 sp. dwarf variety.—2377, 2 sp. with opercula in situ.— 
2378, 12 normal opercula.—2379, 5 do. abnormal, irregular.— 
2380, 4, do. ovate, or with one prong.—2381, 3 do. with two or 
three prongs.—2382, 4 do. with three or four prongs.—2383, 
3 do. with four or five prongs on each side. 
