| 1a |
Length about 1.25 times the height, radial
ribs faint, though
rather broad, and the surface of the shell nearly smooth (length up to
8 cm, but mostly less than 5 cm; subtidal) |
Serripes groenlandicus |
| 1b |
Length decidedly less than 1.25 times the height
(sometimes just equal
to or less than the height); radial ribs pronounced |
2 |
| 2a |
Posterior quarter of valves with rather prominent
concentric ridges
and low radial ribs, so that the sculpture on this part of the shell is
very different from that on the rest of the surface, where only the
closely
spaced radial ribs are distinct |
Nemocardium (Keenaea) centifilosum |
| 2b |
Valves without a substantial area in which the
sculpture differs from
that on the rest of the surface |
3 |
| 3a |
Shell as high as or slightly higher than long; height
up to about 8
cm; common intertidal and shall subtidal species |
Clinocardium
(Clinocardium)
nuttallii |
| 3b |
Length about equal or slightly greater than the height;
height of most
species not exceeding 4 cm (but in C. californiense
it may nearly
reach 7 cm); subtidal |
4 |
| 4a |
Length about equal to the height (height up to about 3
cm; with over
50 radiating ribs, these rather delicate) |
Clinocardium (Clinocardium) blandum |
| 4b |
Length slightly greater than the height (ribs rather
coarse) |
5 |
| 5a |
With 32-38 radial ribs; height usually under 4 cm |
Clinocardium (Clinocardium) ciliatum |
| 5b |
With 40 or more radiating ribs; height may reach or
exceed 4 cm |
6 |
| 6a |
Height up to 7 cm; with about 40-45 ribs |
Clinocardium (Clinocardium) californiense |
| 6b |
Height up to slightly more than 4 cm; with about 45-50
ribs |
Clinocardium (Clinocardium) fucanum |