458 THE OCEAN WORLD. 
small flat head, furnished with lateral tentacles or horns, bearing the 
eyes upon an external swelling, situated near their central length. 
We need only refer to Fig. 288, Buccinum senticosum, and Buccinum 
undatum, the well-known whelk of our markets (Fig. 28g), for their 
general form. ; 
The genus arpa contains shells from the Indian Ocean, richly 
enamelled within, and ornamented externally with slightly oblique 
longitudinal stripes in gay colours, with finely-sculptured forms in the 
intervals; spire very small, and opening large. Among the more 
Fig. 290.—Harpa ventricosa (Lamarck). Fig. 291.—Harpa imperialis (Lamarck). 
attractive species are Hara ventricosa (Fig. 290), Harpa imperialis 
(Fig. 291), and Harpa articularis (Fig. 292). 
The fifth family, AWuricide, contains Fusus, Pyrula, Triton, and 
Murex, 
The genus A¢urex, or Rock Shells, include a large number ot 
species, all remarkable for their bright colours and somewhat fantas- 
tical and varied forms. They are found in all seas, but become 
larger and more branching in the seas of warm regions. The shell 
is oval, or rather oblong, the spire more or less elevated, its surface 
generally covered with rows of spines, or tubercular ramifications. 
The opening, which is oval, is prolonged in a straight canal, often of 
very considerable length, as in A/urex haustellum (Fig. 293); the 
external edge is often smooth or rippled, the columellar edge some- 
times callous. 
