Muma (1951) divided his newly erected genus Therobates Muma 1951 into
three species groups. One, the bilobatus group, was recognized as
consisting of a single moderate-sized species, currently recognized as
Eremochelis bilobatus (Muma 1951),
which was designated as the type species of Therobates. The
bilobatus group was defined as follows:
Moderate-sized
species. Males with mesal groove of fixed finger distinct, enlarged
basally, and containing one or more distinct carinae or ridges. Apical
plumose bristle of flagellum complex not greatly enlarged or elongated.
Ventral tubular bristles of complex situated in a group in the fondal
notch. Females of the only species known have the genital plates lobate
on the mesal margins. Ectal row of fondal teeth graded in size I, II,
III, IV; mesal row I, III, II, IV.
Muma (1962) subsequently added
those species now known as Eremochelis acrilobatus (Muma 1962)
and
Eremochelis plicatus (Muma 1962)
to the bilobatus group. He also added Therobates arcellus Muma
1962, males of which were later (Muma 1963) shown to be misidentifed
specimens of
Eremochelis bidepressus (Muma 1951).
Females regarded as belonging to Therobates arcellus by Muma (1962)
have subsequently been referred to
Eremochelis insignatus Roewer 1934
(Muma 1963, 1970a). Both
Eremochelis bidepressus and
Eremochelis insignatus Roewer 1934
are current members of the branchi species group. The concept
of the bilobatus group remained largely unchanged despite these additions,
although Muma noted that the size gradation of the fondal teeth is variable
between species and specimens, indicating instability of the character.
Muma (1962) also recognized
what he called the arcus group, characterizing it as consisting of small to
moderate-sized species in which the apical plumose bristle of the flagellum
complex on the chelicera of the male arches over the basal portion of the
mesial groove and is neither enlarged nor flattened, the ventral tubular
bristles of the complex are situated in a row just above the fondal notch,
and the mesial groove of the male's fixed cheliceral finger is a narrow,
shallow groove containing no distinct carinae. The only known female
was described as having opercula that are expanded and lobate at the
ectocaudal angle. Ectal and mesial rows of fondal teeth were reported
to be graded I, III, II, IV or I, II, III, IV in size. Into the
group he placed what are now known as
Eremochelis arcus (Muma 1962),
Eremochelis macswaini (Muma 1962),
and
Eremochelis cuyamacanus (Muma 1962),
without altering his characterization of the group.
Muma (1963) later
affiliated the species now known as
Eremochelis flexacus (Muma 1963)
and
Eremochelis nudus (Muma 1963)
with the arcus group, along with Therobates attritus Muma 1963
(described from a female specimen), which has since (Muma 1970a) been
synonymized with Eremochelis imperialis (Muma 1951),
a member of the imperialis species
group. Muma (1970a) provided a tabular key to the species of the arcus group, but
did not alter the diagnoses of either the arcus nor
bilobatus groups.
Muma (1986) next added
Eremochelis truncus Muma 1986
and
Eremochelis rossi Muma 1986
to the bilobatus group, and listed
Eremochelis flexacus under
the bilobatus group heading, but did not offer a revised concept of either
the bilobatus or arcus groups, and noted that the newly described species
"do not significantly alter" any of the species group concepts.
Muma (1989) combined the arcus
group with the bilobatus group, noting that his newly described species
indicate that the groups cannot be maintained separately. He revised
his diagnosis of the bilobatus group to include taxa in which the
mesoventral groove of the male's fixed cheliceral finger may or may not
contain distinct carinae, and in which the female opercula may or may not be
lobate mesally within the posterior notch, or have lateral pits.
In his key to species groups, Muma (ibid) characterized males of the
bilobatus group as having the following characteristics: Fixed
cheliceral finger with a distinct, elongate, mesoventral or dorsomesal
cavity or slot occupying at least half of finger length; apical plumose seta
of flagellum complex obscurely or not widened and flattened. Females
opercula provided posteriorly with a distinct mesal notch and commonly
provided with anteriolateral pits and often with adjacent distinct mesal
lobes at the anterior end of the notch. He added
Eremochelis cochiseae Muma 1989,
Eremochelis giboi Muma 1989,
Eremochelis kerni
Muma 1989, and
Eremochelis noonani Muma 1989
to the newly expanded bilobatus group, and
Vázquez
(1991) added
Eremochelis lagunensis Vázquez 1991.
The bilobatus species group, as currently recognized,
thus consists of the
following taxa:
Eremochelis acrilobatus (Muma 1962)
Eremochelis arcus (Muma 1962)
Eremochelis bilobatus (Muma 1951)
Eremochelis cochiseae Muma 1989
Eremochelis cuyamacanus (Muma 1962)
Eremochelis flexacus (Muma 1963)
Eremochelis giboi Muma 1989
Eremochelis kerni
Muma 1989
Eremochelis lagunensis Vázquez 1991
Eremochelis macswaini (Muma 1962)
Eremochelis morrisi (Muma 1951)
Eremochelis noonani Muma 1989
Eremochelis nudus (Muma 1963)
Eremochelis plicatus (Muma 1962)
Eremochelis rossi Muma 1986
Eremochelis truncus Muma, 1986
