VIII 
SUMMARY, 
MOLLUSCA. Many of the families of this order are destitute of 
shell: the following characters will direct to the Families an 
Genera in which the native species are contained : 
The shell formed in separate pieces, placed transversely across t > 
dorsal surface : Chiton. , . ^ 
The shell of one depressed or conical piece, destitute of convolntio • 
In one or two of the genera, the summit is a little bent, and in atiotlie • 
the internal cavity has a spiral plate: comprizing the Genera 1 ate r 
Emarginnla, Fissurella, Pileopsis, Calyptrtea, Ancylus. 
The shell inflated, aperture wide, the length of the shell, no Columcu 
or projecting spire : Bnlltea, Bulla. P 
The shell thin, depressed, the spire short, last whorl large, aperttn 
large, oval: Vitrina. . „ . -j e 
The shell depressed and earshaped, the spire small, aperture wi< 
oblong, margins separated: Sigaretns, which is distinguished tioru 
Naticl and Neritina, by its more depressed form, by the width of tl> 
aperture, and the want of the umbilical callosity. ■„ 
The shell spiral somewhat depressed, aperture rounded, the m?rg 
disunited, by the projection of the largest whorl without a canal : Hell*: 
Zonites, Suceinea. . . . ... M 
The shell spiral, elevated, aperture entire, the margins disunited 3 
the projection of the largest whorl, no canal : Bulimus, Zua, Pupa» 
Vertigo, Balca, Carychium. ,. prS 
The shell spiral, elevated, slender, aperture irregular, with the bordei 
united, the lowest whorl not the largest : Clausilia. The other f 
of spiral shells, without a canal, will he found m the Genera CydMtom 
Limneus, Nerita, Natica, Ianthina, Tornatell la, Margo ella, V olut^ 
Terehellnm, Turbo, Scalaria, Trochns, Cingula, Phasianella, limit 
With the spire very much depressed, Planorbis. Skenea. 
Spiral shells, with a canal leading from the aperture : Centlunm, I 
rotoma, Fnsiis, Triton, Purpura, Buccinum, Terebra. 
Spiral shells, with a canal and an expansion into a wing ot tn 
outer border of the aperture: Rpstellaria. . .. . 
The shell oval, spire scarcely visible, aperture longitudinal, narro 
toothed on both sides, the extremities effuse : Cvpra?a. 
CEPHALOPODA, oa CUTTLEFISH TRIBE. Some of the family 
of this order have no shell; others have it only internal. In 
family of Orthocerata, the shell is straight, or nearly so, with n 
ternal chambers, perforated by a tube: Orthoccra; easily to 
distinguished from Vermetus, and Serpulace®, by the inter" 
divisions. As is also the genus fspirula which in outward fo » 
approaches to the shape of Spirorbis, but in which the volutions 
not touch each other. . „,i v of 
The characters of the separate Genera will be found in the bo 3 
the work. 
