178 MAirUAL OF THE MOLLTJSCA. 



Shell, mucro cliambered and siphuncled ; ■without lateral -wings 

 or elongated beak. 



Helicertjs, Dana. 



Example, H. Fugiensis. Only siDecies known. 



Shell like a belemnite, half-incli in diameter ; guard thick, 

 Bub-cylindiical, fibrous ; jphragmocone slender, terminating in a 

 fusiform spiral nucleus. In slate rock, Cape Horn. 



Family YI. — SpiRULrDJE. 



^/^e?? entirely nacreous ; discoidal ; "wliorls separate, cbambercd 

 {polythalamous), ■with, a Tentral siphuncle. 



Spirtjla, Lam., 1801. 



Synonym, Lituus, Gray. 



Example, S. Icevis (Gray). PI. I., Fig. 9. 



Body oblong, with minute terminal fins. Mantle supi^orted 

 by a cervical and two ventral ridges and grooves. Arms with 

 six rows of very minute cups. Tentacles elongated. Funnel 

 valved. 



Shell placed vertically in the posterior part of the body, -with 

 the involute spire towards the ventral side. The last chamber 

 is not larger in proportion than the rest ; its margin is organically 

 connected ; it contains the ink-bag. 



The delicate shell of the spirula is scattered by thousands on 

 the shores of New Zealand ; it abounds on the Atlantic coasts, 

 -vnd a few specimens are yearly brought by the GuLf-stream, 

 /nd strewed upon the shores of Devon and Cornwall. But the 

 /nimal is only known by a few fragments, and one perfect 

 specimen, obtained by Mr. Percy Earl on the coast of New 

 Zealand. 



Distribution, 3 s]3ecies. All the warmer seas. 



Order II. — Tetra:brai^chiata. 



Animal creeping ; protected by an external shell. 



Head retractile within the mantle. Eyes pedunculated. 3fan- 

 dihJes calcareous. Arms very numerous. Body attached to tho 

 shell by adductor muscles, and by a continuous horny girdle. 

 Branchice four. Funnel formed by the union of two lobes, which 

 do not form a complete tube. 



Shell external, camerated (polythalamous) and siphuncled ; the 

 inner layers and septa nacreous ; outer layers porcellanous.* 



* The Chinese carve a variety of patterns in the outer opaque layer of the nautilus 

 Bhell, relieved by the pearly ground beneath. 



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