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 irregularis, juniore kaud turritelloidcd. Oper- 

 culum tenuc, concavum, kaud laminatum. 



SECTION A. SPECIES TYPICI. 



Qperculovalde concavo, vix spirali. Species oceanis Atlantico 

 et Orientalibus repertce. 



B. SUBGENUS ALETES. 



Operculo parum concavo, multispirali, 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. 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 CENTIQUADEUS, Vol. 



A. t. magnd, pallide, interdum intensius rufo-fusca ; anfr. 

 nucleosis parvis, Icevilus, glolosis, spird vix monstrante ; dein 

 anfr. rapide augentibus, scparatis ; inter dum irregulariter 

 spiralibus, ad ang. 25, interdum varie contortis ; seu segregates, 

 seu glomeratis ; concMs et rupibus parum affixd, facile separata ; 

 superficie plerunu^ne spiraliter dense rugosd, lineis incrementi 

 transfer sis decussantibitx, interstitiis subprofunde punctatis : 

 pagind omnino inferiore et interdu/n, testa adultd, totd superficie 

 sculpturd obsoletd ; basi interdum planatd, angulatd ; transver- 

 son interdum septo concavo divisd. 



Operculo parvo, dimidio apertures ceguante ; extus concavo ; 

 in medio laviore, structure vix conspicud, apice planato ; margi- 

 nem versus multispirali, marginibus anfractuum haud plurimo- 

 Aug. 1856. cc 



