MAZATLAN UNIVALVES 301 
they be determinately referred to the shells. The two are 
therefore described separately, leaving their union to future 
researches. The arrangement of generic sections is simply 
provisional. 
Genus SIPHONIUM, Browne. 
Testa valde ivregularis, juniore haud turritelloided. Oper- 
culum tenue, concavum, haud laminatum. 
SEcTION A. SPECIES TYPICI. 
Gnereulo vaide concavo, viz spirali. Species oceanis Atlantico 
et Orientalibus reperte. 
B. Susaznus ALETES. 
Operculo parun concavo, multispiraii, sepe iwregulariter 
formatum. 
It might have been thought that the turritelloid opercula 
would have belonged to the turritelloid shells. Such however 
is not found to be the case; the opercula of V. lumbricalis, 
Hindsii, &c. being formed on the laminated type, with a very 
large outer whirl. Without a knowledge of the animals or the 
opercula, these shells can hardly be separated even specifically 
from those of Siphonium proper and Serpulorbis. 
352. ALETES CENTIQUADRUS, Val. 
A. t. magna, pallidé, interdum intensius rufo-fuscd ; anfr. 
nucleosis parvis, Levibus, globosis, spird vie monstrante ; dein 
anfr. rapide augentibus, separatis ; interdum irregulariter 
spiralibus, ad ang. 25°, interdum varie contorits ; seu segregatis, 
seu glomeratis ; conchis et ruptbus parun affix4, facile separate ; 
superficie plerumque spiraliter densé rugosd, lineis increment 
transversis decussantibus, interstitiis subprofunde punctatis : 
pagind omnino inferiore et interdum, testa adulta, tota supenficte 
sculptura obsoletd ; bast interdum planaid, angulata ; transver- 
sim interdum septo concavo divist. 
Operculo parvo, dimidio aperture equante ; extus concavo ; 
in medio leviore, structura vie conspicud, apice planato ; margi- 
nem versus multispirali, marginibus anfractuum haud plurimo- 
Aug. 1856. ce 
