| 1a |
Height about 3 times the diameter; siphonal
canal about half the total length of the aperture |
Exilioidea rectirostris |
| 1b |
Height less than 3 times the diameter; siphonal
canal usually less than half the total height of the aperture |
2 |
| 2a |
Height of aperture
about four-fifths the height of the shell |
Volutharpa ampullacea |
| 2b |
Height of aperture
not more than two-thirds the height of the shell |
3 |
| 3a |
Outer lip of aperture
curving convexly until it reaches the tip of the siphonal
canal (it may, however, be slightly sinuous, especially in
species
that have spiral
ridges on the body
whorl) |
4 |
| 3b |
Outer lip of aperture
generally with an obvious indentation just above the siphonal
prolongation |
5 |
| 4a |
Height of aperture,
including the siphonal
canal, about half the height of the shell; spiral
ridges pronounced, convex, some of them not much wider than
the furrows
between them; periostracum
largely limited to the furrows between the ridges; with or without axial
ribs
B. undatus Dall, 1919, which has axial
ribs, is here considered to be a synonym |
Beringius crebricostatus |
| 4b |
Height of aperture
slightly more than half the height of the shell; spiral
ridges, if prominent, not markedly convex and much wider than
the furrows
between them (in some specimens, spiral
ridges are evident only on the body
whorl); without axial
ribs (periostracum
fibrous, abundant, and usually continuous) |
Beringius eyerdami |
| 5a |
Shell smooth or with closely spaced, contiguous spiral
ridges, all
ridges on a particular whorl being of about the same size (axial ribs
may
also be present); whorls without angular shoulders |
6 |
| 5b |
Shell either with widely spaced spiral ridges (these
may be restricted
to the upper whorls) or with spiral ridges of decidedly different
sizes;
whorls usually with angular shoulders |
10 |
| 6a |
Without axial ribs, with or without closely spaced
spiral ridges (includes
one fairly common subtidal species, Colus halli |
7 |
| 6b |
With rather prominent axial ribs, as well as with
closely spaced spiral
ridges (rare subtidal species) |
9 |
| 7a |
|
|
| 7b |
|
|
| 8a |
|
|
| 8b |
|
|
| 9a |
With about 23-28 axial ribs on each whorl; height up to
3 cm |
Plicifusus griseus
(Now = Colus
griseus
in family Buccinidae) |
| 9b |
With 12-15 axial ribs on each whorl; height up to 1.8 cm |
Mohnia frielei |
| 10a |
|
|
| 10b |
|
|
| 11a |
|
|
| 11b |
|
|
| 12a |
|
|
| 12b |
|
|