268 



COLLEGE ZOOLOGY 



Order i. Tetrabranchia. Cephalopoda with four gills, four 

 kidneys, and four auricles; with a large, external shell; no 

 suckers; and very short arms. Example: Nautilus (Fig. 194). 



6 



--8 



'--9 



Fig. 194. — The chambered nautilus, Nautilus pompilius. i, last com- 

 pleted chamber of shell; 2, hood part of foot; 3, shell muscle; 4, mantle cut 

 away to expose, 5, the pinhole eye; 6, outer wall of shell, partly cut away to 

 show chambers; 7, siphon; 8, lobes of foot; p, funnel. (From Shipley and 

 MacBride, after Kerr.) 



Order 2. Dibranchia. Cephalopoda with two gills, two 

 kidneys, and two auricles; with shell enveloped by the mantle; 



and long arms provided with 

 suckers. 



Suborder 1. Decapoda. 

 Dibranchia with ten arms 

 — two long and eight short. 

 Examples: Loligo (Fig. 191), 

 Ommastrephes, Rossia. 



Suborder 2. Octopoda. 

 Dibranchia with eight arms 

 of equal length. Examples: 

 Octopus (Fig. 196), Alloposus. 



Nautili. — There are only 

 a few living species belong- 

 ing to the genus Nautilus in 



Fig. 195. — The paper nautilus, Argo- 

 nauta argo (female), swimming. (From 

 Sedgwick.) 



