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, Broicne. 



Testa valde irregularis, juniore haud turritelloided. Oper- 

 culum tenue, concavum, haud laminatum. 



Section A. Species typici. 



Operculo valde co?icavo, vix spirali. Species oeeanis Ailantico 

 et Orientalibus repertce. 



B. Subgenus ALETES. 



Operculo parum coiicavo, muUispirali, scepe irregulariter 

 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. lumbricabs, 

 Hindsii, &c. being formed on the laminated type, with a very 

 large outer whirl. Without a knowledge of the animals or the 

 opercida, these shells can hardly be separated even specifically 

 from those of Siphonium proper and Serpulorbis. 



352. Aletes centiquadeus, Val. 



A. t. magnCi, pallide, intei'dum intensius rufo-fusca ; anfr. 

 nucleosis parvis, lavihus, globosis, spird vix monstranie ; dein 

 anfr. rapide augentibus, separatis ; interdum irregulariter 

 spiralibus, ad ang. 25", interdum varie contortis ; seu segregatis, 

 seu glomeratis ; conchis et rupihus parum affixa,facile separata ; 

 superjicie plerumque spiraliter dense rugosA, lineis incrementi 

 transversis decussantibus, interstitiis subprofunde punctatis : 

 pagind omnino inferiore et interduyn, testa adultd, totd superjicie 

 sruljjturd obsoletd ; basi interdum planatd, angulatd ; transver- 

 sim interdum septo concavo divisd. 



Operculo parvo, dimidio apertures cequante ; extus concavo ; 

 in medio Iceviore, structurd vix conspicud, apice planato ; m,argi- 

 nem versus muUispirali, marginibus anfractuum haud plurimo- 



Aug. 1856. cc 



