72
Rock-pocketbook, Arcidens confragosus
Description: [I have not seen or
handled a fresh specimen so my
description is based on two
archeological specimens and Internet
photos.] To me, the Rock pocketbook
looks like a cross between a
Threeridge and a Mapleleaf. It is
squarish, has a sulcus next to the
posterior ridge and has numerous
pustules and bumps like the
Mapleleaf. They can also have large
posterior ribs like those of the
Threeridge. The nacre is white. The
exterior can be green or tan in
juveniles, darkening to dark brown in
adults. The beak sculpture is a series
of coarse ridges which are sort of W-
shaped. There are lateral and
pseudocardinal teeth which are
similar to but finer than those of the
Mapleleaf.
Similar species: Similar in shape
and size to a Mapleleaf but thinner
and with distinctively different beak
sculpture. Vaguely similar to a
Threeridge.
Conservation status: G4, N4, SX.
Their status in Nebraska is
indeterminate. They were assumed to
have been extirpated until the recent
collection of some dead shell from the
Missouri River.
Hosts: American eel, channel catfish,
freshwater drum, gizzard shad, rock
bass, white crappie.
Habitats used: Medium to large
rivers in pools and areas of reduced
flow in mud and sand (Cummings and
Mayer 1992). Large rivers in soft
substrates (Seitman 2003). Quiet
areas of rivers in soft mud (Oesch
1995). Medium to large rivers in areas
with reduced current and substrate of
mud or mud and fine sand (Parmalee
and Bogan 1998). Muddy sand and
silt in rivers (Watters et.al. 2009).
Native range: The Mississippi River
basin from Ohio to Kansas down to
Texas over to Alabama and up to
Minnesota
Nebraska collection notes: This
species has been found as relict shell
in Logan Creek in the Elkhorn River
basin. Dead shell were found in 2000
in the Missouri River below Gavins
Point Dam. Specimens of this species
have been identified from
archeological sites in Douglas and
Washington counties indicating
possible historical presence in the
state.
Comments: I have only seen the two
archeological specimens illustrated on
the photo page. This species has
always been extremely rare in
Nebraska but there may still be a few
in the Missouri River.
