94 MOLLUSCA. 
« In the course of our review of the Linnzan genera of 
bivalves, we have exposed some of those errors which the 
Swedish naturalist committed in associating discordant spe- 
cies under the same genus. Perhaps our examination of 
the univalves will make us better acquainted with the im- 
perfections of that system, and dispose us to prize those im- 
provements which subsequent naturalists have introduced. 
18. ArconauTa. This genus, which contains but few 
species, is highly prised by collectors, who call the princi- 
pal species by the name of paper nautilus. By restricting 
the characters of this genus, so as to embrace only those 
species in which the opening is interrupted by the involu- 
tion of the spire, and in which the dorsal ridge is double, 
Lamark has been able to form the genus CartnartA. In 
this the mouth is entire, and the dorsal ridge single. It is 
represented by the argonauta vetrea of Gmelin. 
18. Nautiius. Since the days of Linneus, our know- 
ledge of the multilocular testacea has been greatly enlarg- 
ed. He contented himself with arranging all the species 
with which he was acquainted under one genus, but, in con- 
sequence of modern industry, even the genera exceed the 
number of Linnean species. Many recent species have 
seen discovered by the aid of the microscope, among the 
sand on the sea shore, and a still greater number in a fossil 
state among the calcerous strata. These newly discovered 
kinds exhibit many different characters, and have compell- 
ed conchologists to institute so many new genera for their 
reception, that the genus Nautilus of Linnzeus appears rather 
as the head of a family or order, than as a separate genus 
of univalve shells. In this department the names of Bru- 
guiére, Lamark, Montfort, Parkinson, and Sowerby, deserve 
respectful notice ; and it is from their writings that the fol- 
