1 42 UNIVALVES TROCHUS. 



ture of the shell in this as well as in many other genera of 

 univalves, is closed by a stony or horn-like operculum, 

 affixed to the animal. 



Of the divisions of the Trochus the first is the most 

 numerous; it comprehends those species which have 

 their pillar perforated, and is divided into five fami- 

 lies, distinguished by the peculiarities of the pillar 

 and umbilicus : the T. niloticus, T. maculatus, T. pha- 

 raonis, T. cylindraceus, and T. perspectivus, may be 

 mentioned as illustrative examples of each family. 



The T. conchyliophorus, or Carrier Trochus, is a very 

 remarkable species ; it is invariably covered with ex- 

 traneous substances, strongly adhering to the whorls 

 of the shell. There are two distinct varieties : one of 

 which is familiarly called the Conchologist, from its 

 being loaded with perfect shells or fragments ; and the 

 second, the Mineralogist, as its adhesions consist of 

 stones, ores, &c. When the former variety is loaded 

 with corals only, it is called the Zoologist or Coral- 

 carrier. 



The second division consists of those Trochi which 

 are imperforated, or have their umbilicus closed, as in 

 the T. tuber, (which greatly resembles a Turbo) T. labio, 

 and T. vestiarius. The T. iris of this division deserves 

 particular notice, on account of the iridescence and 

 splendid metallic lustre which its surface exhibits when 

 uncoated. 



The third division includes those species which are 

 much elongated, and greatly resemble screw or needle 

 shells. Unlike the rest of the genus, they have an ex- 

 serted pillar; and, when placed on their base, they fall 



