1*01; TKTKAHi: AN< HI ATA. 



It' we regard strictly tin- rules <>t' priority, lliis species will 

 bear the name of S. (Nautiltix) .</,;/>//</. Linn.: whilst those of 

 8. prototypUS, IVron. Mini N. frnijili*. L:iin.. are both antecedent 

 to S. Pcronii. I allow the hitter name lo stand because it is s<> 

 well known that to displace it in favor of either of the other- 

 would create uncertainty and confusion. It may be remarked 

 that two pre-Linneao authors perceived its ivnerie distinctness 

 from Nautilus with which Linmeus confounded it: aud one o! 

 1 IK-HI. Browne, Only published a year loosoon to have his o-cnerie 

 name of />//////> adopted. 



II. TETRABRANCHIATA. 



Animal breathing by two i>airs of internal, symmetrical Ljill-> 

 or branchhe. 



Kyes pednnciilate(l. Mandibles calcareous. A rms (tentacles ) 

 \cry numerous, not provided with sucking disks. I>ody a : taclied 

 to the shell by adductor muscles and the mantle 1>\ a conlimious 

 horny girdle. Siphon an incomplete tnl>e formed l>y the union 

 of two lobes. No ink-bai--. ( 'i-eepinu,-. and protected by an ex- 

 ternal concameraU'd shell, the last chamber of -which it inhabits. 



Shell formed of two layers, the external porcelanous. the 

 intei'iial and the sepia or partitions nacreous. Partitions pierced 

 by siphon-lubes. 



Nearly two thousand fossil species of cephalopods have been 

 referred to the t et rabrandiiat es. alt houi>'h it has been recently 

 suspected that at lea-! a lariv portion of these were internal 

 shells like t he Spirulas and jvfei'able therefore to ! he dibranchiata. 

 Only :i hail-doxeii recent s))ecies are known: all belonu'm 

 the Li-enus Ntni/ilii*. 



Tin- tetrabranchiate shell is essentially an elongated cone. 

 divided otf into chambers by partitions, and siphunciil; 

 These septa ha\c simply curved ed^-es in Xfmlilu* and Orlli't- 

 -. the\ are xiu-xajj. in G<>ni<il it<-*, ( foliaceous. forming com- 

 plicated l<bes in Ainiiiniui''*. 'I'he shell may be st raio'ht . curved. 

 open or rlo-r spiral, and even vary in form at ditfereiit aii'es. and 

 variations, when well understood, will doubtless cause a 

 reduction to be made in the number of uvneric forms at 



