TROCHUS 



TESTA conica, spira plus miniisve elata, periphe- 

 ria pleriirnque angulata, interdum rotundata ; 

 apertura plus minusve trans versim depressa, 

 subtrapeziformi ; columella arcuata, basi plus 

 minusve prominula ; operculo corneo, eirculari, 

 spirali, anfractibus plurimis, confertis* 



So little attention having been formerly given to natural 

 affinities, it is not surprising that in consequence of a 

 certain accordance in general form, Linne and subsequent 

 authors should have combined together shells of very 

 various and distinct characters, while they separated 

 others naturally allied to each other. Though this ob- 

 servation is more particularly applicable to Linne and 

 his disciples, it must also be acknowledged that later 

 authors, whose general endeavours have been sucessfully 

 directed to the improvement of natural science, have to a 

 certain degree fallen into the same error; thus Lamarck, 

 attending too much to external form has united in Trochus 

 shells which are not related to each other: for though in 

 the character he gives of the Genus, and indeed of the 

 family, he mentions an operculum as essential, he has 

 united to it several, e. g. (his T, radians^ Pileus and 

 T, CalytrcBforniis) which have no operculum ; we observe 

 also that several others, which are admitted by Lamarck, 

 differ from the greater part of his Trochi in having a thick 

 shelly operculum, while several whose operculum is like 

 tliat of Trochus Niloticus and which should consequently 

 be united to the Trochi, are found among the Turbines; 

 whereas the only certain character by which the Trochi 

 can Jbe separated from the Turbines consists in the former 

 having a horny, the latter a shelly operculum. That the 



