310 MAZATLAN UNIVALVES 
Tablet 1499 contains 6 sp. broken so as to shew the internal 
laminee.—1500, a mass almost covering Murex princeps, with a 
?Sphenia in avarical foliation.—1501, Uvanilla olivacea, with 
several specimens attached.—1502, 2 sp. of U. unguis, do.— 
1503, Leucozonia cingulata, do.—1504, 3 sp. Cuma costata, do. : 
in one, the P. macrophragma has been removed, shewing the 
amount of erosion.—1505, Rhizocheilus nux, Pisania gemmata, 
and Columbella fusca, do.—1506, Omphalius ligulatus and 
Fissurella rugosa, do. 
Opercula of Vermetide. 
(a.) Operculum o. “ Alete centiquadre” simile, sed magis 
regulariter multispirale ; extus parum concavum, marginibus 
anfractuum levibus, parum extantibus, umbone centrali elevata ; 
superficie anfr. circiter vill., umbone iv. instructis ; intus cica- 
trice magna irregulariter concentricé rugosa. 
"Tablet 1507 contains one of three opercula, probably belong- 
ing to a second species of Aletes. 
(b.) Operculum spirale, corneum, subolivaceum, tenue ; extus 
parum concavum, marginibus valde tenuibus, haud regularibus ; 
anfr. circiter xv. haud distincté definitis, haud extantibus, ad 
apicem haud umbonatum ascendentibus ; intus cicatrice parvo, 
vie corrugato. 
Tablet 1508 contains two opercula, which probably belong 
to an Aletes. 
(c.) Operculum haud parvum, haud regulare, cornewm, tenue, 
diaphanum ; extus subconcavum, laminis parum elevatis, um- 
bone extante: intus via convexum, liris ?concentricis multis 
subdistantibus, subextantibus, margine parvo ; cicatrice parva, 
irregulariter concentricé rugosa. 
Tablet 1509 contains an operculum, in poor condition, inter- 
mediate between Aletes and Vermetus proper; remarkable 
fer the internal ridges, which are not crowded into the middle 
portion, and leave a comparatively small margin. 
(d.) Operculum distincté spirale, tenue, corneum, diaphanum ; 
extus marginibus parun convexis ; lamind concava soluta, levi, 
acuta, spiraliter ascendente, anfr. internis conveniente, apice 
parum elevato, vix umbonato : intus parum convexnm, triente 
interné anfr. multis ; trientibus duabus externis anfractu ultime 
oceupatis ; cicatrice vie corrugata. 
