ing the rostral nerves (grn). The lateral ethmoid
shelves are penetrated several millimeters from the
lateral edge by foramina carrying nerves to ampul-
lary organs of the dorsal rostrum (nfand arrows,
Figure 17d). Size and shape of the rostrum varies,
but expanded lateral ethmoid shelves are present in
all scaphirhynchines.
In all species ofAcipenserexamined, the lateral
ethmoid ridges end in a thin ventral edge (Figure
17c).No foramina penetrate these lateral ethmoid
ridges, suggesting that cartilage is added lateral to
the foramina in scaphirhynchines. SinceHusoand
polyodontids do not possess lateral ethmoid ridges,
this is a two taxon statement at the generic level, but
1 accept the flattened morphology of scaphirhyn-
chines as derived. The cylindrical head ofHusosug-Figure 23.Caudal fin endoskeleton ofHuso husoandScaphirhynchus platorynchus: Anterior faces to left. Hypurals (hyp) are stippled
lightly while the more anterior basiventrals (bv) and basiventraIs with haemal spine (bvh) are dark. Basiventrals with haemal spines
overlap the anal fin inHuso, but are restricted to the caudal fin in acipenserines (Character 38). The elongate caudal peduncle of
Scaphirhynchus(b; (Character 64) displaces the dorsal and anal fins anteriorly, but possessing only three-four basiventrals with haemal
spines is typical for acipenserines. The notochord and bracketing cartilages end in unison inHuso(a) andAcipenser,but a cartilaginous
core supporting the cercus continues in scaphirhynchines (Character 53) beyond the terminus of the notochord.bd= basidorsals,sn=
supraneural homologs.