Z OLIVA. 



It lias fallen to tlie Editor's lot to translate and put into 

 form corresponding to the general plan of the work, the 

 valuable results of Mr. Marrat's labours. He has not in 

 any case interfered with the insertion and arrangement of 

 species adopted by the author. In some few cases, how- 

 ever, he has ventured to express an opinion ; and wherever 

 the opinion so expressed has not coincided with the author's 

 views, he has distinguished his own remarks by the letters 

 " Ed." 



Genus OLIVA. 



Molluscum trachelipodom. Testa porcellana, oblonga ; 

 anfractu ultimo magno, antice rima elevata. balteato ; aper- 

 tura angusta ; columella medio et postice plus minusve cal- 

 losa, plicata, antice callo spirali plicato terminauti ; spira 

 plerumque brevi ; sutura canaliculata. 



Operculum in speciebus majoribus cyliudraceis nullum ; 

 in minoribus ancillariformibus plurimis elongatum, corneum, 

 nonspirale, nucleo subterminali laterali. — Ed. 



Shells varying from oblong-cylindrical to broadly-fusi- 

 form ; spire from flat or depressed to very elongately conical ; 

 sutural canal either wholly or partially open ; columella either 

 plaited or having oblique folds at the base ; shells smooth, 

 generally highly polished. Species resembling the following 

 genera are found among the Olives, viz. Aucillaria, Conus, 

 Mitra, Marginella, etc., from all of which they may be dis- 

 tinguished by the open sutural groove. — F. P. Marrat. 



If it could be ascertained, with anything approaching pre- 

 cision, that the shells of any large group, agreeing with each 

 other in form, possessed an operculum, while another sec- 

 tion, agreeing in other general characters, did not, we 

 should then have good grounds for generic or subgeneric 

 division. But this is not the case. The gradations in respect 

 to form, proportions, spiral and anterior callosities, etc., are 

 so minute and variable, and depend so much upon age and 

 condition of specimens, that the subgeneric divisions pro- 

 posed by authors cannot be defined. 



The larger, more cylindrical, solid shells have been 

 divided, without any appreciable line of demarcation, into 

 the groups or subgenera Porphyria, Bolt., Cylindrus, Meu- 

 schen, Ispiddxa, Gray. None of these are operculated. 



