CHARACTERISTIC DEEP-SEA TYPES. — GASTEROPODS. 71 
Another illustration of the fragile and delicate forms living 
in the abysses is Triforis longissimus (Fig. 295), only thir- 
Fig. 205. — Triforis longissimus. 2, 
teen hundredths of an inch in diameter, with a column of 
twenty or thirty whorls, reaching an inch to an inch and a 
half in length; the perfect shell must have over forty turns, 
but it is always decapitated. Siliquaria modesta (Fig. 296), 
Fig. 296. — Siliquaria Fig. 297. — Vermetus 
modesta. 15, erectus, 45, 
1 
one of the irregular gasteropods, with a slit like a Pleurotoma- 
ria, so frail as almost to perish with a touch, lives in the soft 
mud of the abysses, while the stouter Vermetus erectus (Fig. 
297) finds a foothold on dead corals and shells. The species 
of this genus are comparatively shallow-water animals. 
The majority of the bivalves are characterized by great deli- 
cacy of shell and sculpture. In the deep-water representatives 
of the family of scallops, the constituent prisms are often large 
enough to be seen with the naked eye, and the shell is strength- 
ened within by slight riblets radiating from the hinge. Pecten 
