MANUAL OF CONCHOLOGY, 



FAMILY TROCHID^. 



Animal similar in general form to the Turbinida?. Epipodial line 

 bearing one, several, or many smooth or ciliated cirrhi on each 

 side; head with a short, broad rostrum ; intertentacular lobes sim- 

 ple or digitated, separate or united across the front, sometimes obso- 

 lete. Jaws developed or absent. Radula rhipidoglossate, rhachidian 

 teeth always present and well-developed ; lateral teeth generally 5 

 on each side, sometimes more numerous ; marginal teeth narrow, 

 very numerous. 



Shell nacreous within, conical, pyramidal, subglobose, turbinate or 

 helicoid ; aperture entire, tetragonal or rounded ; peristome gener- 

 ally not continuous. Operculum circular, thin, entirely corneous, 

 formed of numerous gradually increasing whorls, nucleus central. 



The TrochidaB are like the Turbinidse in the possession of a na- 

 creous test and in the principal structural characters of the animal. 

 They differ from that family in having a corneous, never calcareous, 

 operculum, which is always multispiral. 



The family is represented by numerous littoral species on nearly 

 all coasts, and numbers also many deep sea forms. 



Since very early times many species have been well-known to 

 naturalists. The name Trochus, according to Fischer was used for 

 the first time by Rondelet, in 1558, who assembles under this title a 

 rather miscellaneous assortment of univalves, including a true 

 Trochus. Linnaeus' genus Trochus is composed principally of true 

 Trochidre, but contains also species of several very different families. 

 Lamarck still further restricted the group by eliminating several 

 genera; and in more recent times the labors of Gray, H. and A. 

 Adams and others, have contributed much toward a systematic ar- 

 rangement of the family. 



The more extensive works upon the Trochidse are the following. 



A. ADAMS. 



Contributions toward a Monograph of the Trochida?, in Proc. 

 Zool. Soc., 1851, pp. 150-192. 

 (5) 



