more elongate than a small, inner tip (Figure 25d).
Larger rakers may possess only an outer tip, but the
base remains expanded where the inner tip would
protrude Gill rakers of P. fedtschenkoi are de-
scribed as lanceolate (Berg 1948) and undescribed
inP. hermanni,but lacking clear description, I ac-
ceptP. Kaufmannias diagnostic of the genus.
Raker shape varies greatly among acipenserids.
Rakers ofHuso, Psephrirus,and several species of
Acipenser(e.g., A. oxyrinchus) are elongate and
lanceolate, tapering from a narrow base to a blunt
tip (Figure 25a). Most other species ofAcipenser
(e.g., A. brevirostrum) possess triangular rakers
(Figure 25b), but none possess rakers with pronged
tips. The crenelated rakers ofScaphirhynchus are
distinct (Character 63) and not comparable toPseu-
doscaphirhynchus.
varies from two to seven and they may fuse in onto-
geny (Findeis 1993), but they collectively occupy an
consistent area (Figure 5d). Localization of the lat-
eral extrascapulars is consistent in all species of Sca-
phirhynchus.
There is a significant variation in the dermal skull
of acipenserids (Parker 1882, Jollie 1980) and posi-
tion, size, and number of the lateral extrascapular
bones is variable. InPseudoscaphirhynchus(Figure
5e; see Character 56) andHuso(Figure 5b), lateral
extrascapulars are typically canal bones. Whereas
Husotypically possesses only canal-bearing lateral
extrascapulars (Figure 5b).Pseudoscaphirhynchus
possesses multiple anamestic bones (Figure5c).All
species ofAcipenserexamined show extensive vari-
ation in number and position of lateral extrascap-
ulars (Figure 5c).Character 59. Clavicles tips meet us an anteromedial
wedge–PseudoscaphirhynchusThe clavicles ofPseudoscaphirhynchus converge
medially as an anteromedial wedge (Figure 26c).
This anterior wedge is externally visible and confir-
mable from photographs in P. hermanni (Berg
1948a). Clavicles ofPseudoscaphirhynchusalso dis-
tinctively possess strong central ridges running
through the anteroposterior axis that possess three
or four spikes inP. Kaufmannni(Figure 26c), but is a
plain ridge inP. hermanni(Berg 1948a).
InScaphirhynchus, Huso, and all species of Aci-
penserexamined, anteromedial edges of the clav-
icles converge more linearly to the midline (Figure
26a, b). The clavicles typically meet in a slight ante-
rior point, but this wedge is not prominent as in
Pseudoscaphirhynchus Also, outgroups do not
possess a robust central ridge, much less any spikes
along the clavicle.
Character 61. Complete circumorbital series present- Scaphirhynchus
The dermal skull roof ofScaphirhynchusis unique
within Acipenseridae in possessing a complete cir-
cumorbital series with contact between the antorbi-
tal (see Character 46) and an enlarged postrostral
bone of the border rostral series (prb, Figure 4e).
With postrostral contact, the antorbital is widened
ventrally with a flat edge. Antorbital shape and post-
rostral presence are also diagnostic of Scaphirhynchus
chus,but correspond to completion of the circum-
orbital series and are subsumed into this character.
Huso, Pseudoscaphirhynchus, and all species of
Acipenserexamined lack a completecircumorbital
series,with the antorbital isolated dorsally. No post-
rostral is identifiable in these taxa as the border ros-
tral series is thin without any expanded bones (see
Figure 18c, d).Character 62. Branchiostegal one is short and trian-
gular – ScaphirhynchusBranchiostegal one is a thin, triangular bone inSca-
phirhynchuswith a flat ventral edge that converges
dorsally (Figure 7e) to contact the subopercle with-
in a broad, vertical groove.Character 60. Lateral extrascupulars are clustered –
ScaphirhynchusLateral extrascapulars form a positionally restrict-
ed cluster alongside the median extrascapular in
Scaphirhynchus(excl, Figure 5d). Number of bones