68 THREE CRUISES OF THE * BLAKE.” 
and very pearly. The shallow-water forms may subsist on stony 
algee or other plants, but the majority are flesh-eaters, or feed 
upon the corallines and foraminifers, parts of whose shells are 
found in their stomachs. 
While not so brilliantly colored, the deep-water Trochide are 
unsurpassed in beauty by their shallow-water allies. They gain 
in delicacy and iridescence what they lose in depth of tint. One 
of the handsomest forms is Calliostoma Bairdii Verrill, whose 
pale, depressed, and more 
delicate southern variety, C. 
psyche, was first dredged by 
Pourtalés. It is, like many 
other species of similar range, 
tinted with pink and straw- 
color, while farther north it 
assumes brown and red livery. 
Even more delicate and pecu- 
liar in the concave outline of 
its granular spire and polished 
Fig. 285. — Calliostoma aurora. 9. base is Calliostoma aurora 
(Fig. 285), of which only a 
single specimen is known, —a genus most characteristic of 
Western America. It seems as if differences of temperature 
and food were indicated in very similar ways between northern 
and tropical animals, whether they live 
in the deep sea or inhabit the land. 
A real treasure of the sea is Gaza 
superba (Fig. 286), one of the most 
beautiful and widely distributed abys- 
sal shells. Were it not for its lovely 
iridescent pearly sheen, it might be 
taken, on a casual examination, for fig. 286. — Gaza superba. 148. 
one of our large straw-colored land 
snails. Other characteristic species, widely distributed, are Mar- 
garita egleés and Leptothyra induta (Vig. 287) of Watson, small 
white shells from deep water, named from examples collected by 
the “ Challenger," and especially illustrating the luxury in vari- 
ation which has already been referred to, and which has led in 
