178 MANUAL OF THE MOLLUSCA. 
Shell, mucro chambered and siphuncled ; without lateral wings 
or elongated beak. 
HELICERUS, Dana. 
Example, H. Fugiensis. Only species known. 
Shell like a belemnite, half-inch in diameter; guard thick, 
sub-cylindrical, fibrous; phragmocone slender, terminating in a 
fusiform spiral nucleus. In slate rock, Cape Horn. 
FAmILty VI.—SPIRULIDA. 
Shell entirely nacreous; discoidal ; whorls separate, chambered 
(polythalamous), with a ventral siphuncle. 
SPIRULA, Lam., 1801. 
Synonym, Lituus, Gray. 
Example, 8. levis (Gray). Pl. I., Fig. 9. 
Body oblong, with minute terminal fins. Mantle supported 
by a cervical and two ventral ridges and grooves. Arms with 
six rows of yery 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, 
and a few specimens are yearly brought by the Gulf-stream, 
md strewed upon the shores of Devon and Cornwall. But the 
animal is only known by a few fragments, and one perfect 
specimen, obtained by Mr. Percy Earl on the coast of New 
Zealand. 
Distribution, 3 species. All the warmer seas. 
ORDER JJ.—TETRABRANCHIATA. 
Animal creeping ; protected by an external shell. 
Head retractile within the mantle. Hyespedunculated. dan- 
dibles calcareous. Arms very numerous. Body attached to the 
shell by adductor muscles, and by a continuous horny girdle. 
Branchie 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 
shell, relieved by the pearly ground beneath. 
