68 



THREE CRUISES OE THE ''BLAKE. 



and very pearly. The shallow-water forms may subsist on stony 

 alga? or other plants, but the majority are flesh-eaters, of feed 

 upon the corallines and foraminifers, parts of whose shells are 

 found in their stomachs. 



While not so brilliantly colored, the deep-water Trochidae 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 

 Pourtales. 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 

 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 

 one of our large straw-colored land 

 snails. Other characteristic species, widely distributed, are Mar- 

 garita ceglees and Leptothyra induta (Fig. 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 



Fig. 285. — Calliostoma aurora. 



Fig. 286. — Gaza superba. 



