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<br />
<br />II ubbs and J.lf iller
<br />
<br />Hybridization between Catostomus and Xyrauchen
<br />
<br />221
<br />
<br />(p. 216). In Catostomus latipinnis both upper and lower lips are
<br />very full (Girard, 1859, pI. 24, figs. 1-2). The upper one is strongly
<br />pa.pillate over a broad turgid surface; the lower lip is narrowly
<br />separated at the extreme base, and the lobes become very mark-
<br />edly elongate with age, suggesting the vernacular name, "fIannel-
<br />mouth sucker." The gape widens less markedly with age than it
<br />does in Xyra1.lchen. It remains narrowly instead of broadly u-
<br />shaped. As a. result of the lengthening of the lips in C. latipinnis
<br />and the widening of the gape in X. texanus, the mouth proportions
<br />(Fig. 3) become increasingly and very notably divergent. Con-
<br />versely, with decreasing size, the differences diminish, until at about
<br />35 mm. standard length the measurements are very :similar and the
<br />structure is not strikingly different. The distinction between the
<br />genera involves chiefly the retention in Xyrauchen of juvenile lip
<br />structures. The upper lip in that genus remains relatively narrow
<br />and less swollen in longitudinal section. It has tewer series of
<br />papillae, which are lower and flatter, and is more definitely angulated
<br />along the single main row of developed papillae. The lobes of the
<br />lower lip remain well separated to the extreme base and do not be-
<br />come greatly elongate, and the inner edges of the gape remain more
<br />distinct (PI. IV, C; also Simon, 1946, fig. 25, 4).
<br />Intermediacy is also seen in the degree of coiling of: the intestines.
<br />In adults of Catostornus latipinnis the region of coiling extends to a
<br />point opposite the outer part or end of the pectoral fin; in the larger
<br />hybrids it extends to a point between the pectoral tip and the pelvic
<br />insertion; and in adults of Xyrauchen texanus it extends more or less
<br />beyond the pelvic insertion.
<br />There are strong indications of rather variable intermediacy in
<br />coloration, also. The hybrids approach Xyrauchen in the dark tone
<br />of the sides of the body and head and in the relative uniformity of
<br />pattern in the dark areas of the body (that is, in the weakness of
<br />the characteristic sucker mottling). They appear to be intermedi-
<br />ate, also, in the degr'ee of contrast between this dark color and the
<br />brightly whitc lower parts, and in the contrast between the dark
<br />borders and the light centers of the scale pockets. These interme-
<br />diate characters are definitely exhibited by the larger hybrids (PI.
<br />I, Fig. 2), which are fresh and well preserved, and are faintly re-
<br />tained in the old, faded type of X. uncompahgre.
<br />
<br />STATUS OF XYRAUCHEN UNCOMPAHGRE
<br />
<br />From the data here presented it is clear that the holotype of
<br />Xyrauchen uncompahgre is intermediate in nearly all characters
<br />between Catostomus latipinnis and X. texanU9 and is definitely to be
<br />regarded as a hybrid. Gilbert and Scofield (1898, p. 492) therefore
<br />erred in stating that it agrees with the young of Xyrauchenin all
<br />characters except the number of dorsal rays, and in concluding that
<br />X. 1lncompahgre will probably be found to be the same as X. cypho
<br />(= X. texanus).
<br />
<br />Catostomus insignis X Xyrauchen texanus
<br />
<br />(PI. IV)
<br />
<br />U.M.M.Z., No. 167095: six young specimens 54-78 mm. in stand-
<br />ard length, collected by Carl L. and Laura C. Hubbs and I....eonard
<br />P. Schultz aboutmidway between Roosevelt Dam and Payson, Gila
<br />County, Arizona, in the lower part of Tonto Creek, a tributary of
<br />Roosevelt I~ake, which lies in the course of Salt River of the Gila
<br />River systcm; September 15, 1926.
<br />
<br />RELATIVE NUMBERS OF HYBRIDS AND PARENTAL SPECIES AND
<br />SPAWNING RELATIONS
<br />
<br />In terms of the effective breeding populations, the relative num-
<br />bers of Catostomus insignis (Table VI) are overweighted and those of
<br />Xyrauchen underweighted, both for the Tonto Creek collection con-
<br />taining the hybrids and for the combined samples from the whole
<br />basin, because most of the collections were made in the smaller
<br />streams, where Catostomus is more permanently resident. The huge
<br />adults of Xyrauchenobviously live most of their)i~esin,the!larger,
<br />dee?er waters. : r,' ~o~~~dY1i,the~i~~,~s~~,' 'ffliU~,~~~~~,~~4~~~~e
<br />~,mamchan~els'o~therl~erand,ltsJarger '" "l~s~(J:or~~~'$l891l'
<br />~tp :26) ;verY')$r~l>~~Iy'iii,;deepe< hoies,a#~~." .'nie\vh~ti,"Bhe~ter~d
<br />~;:~ituatio~s:~~~~~l~te~tiilion~_,~ep~r~ed~~~~\J~;~ ,~~,~(18?1!j~ftfK~P)t;~~d
<br />r,~?~6~' iis""i~di~a t~s,th~t,t?e.".specles i.once, untlertobk,ra ther\extilnsl re
<br />Wrlpst:re\l.Ji''sp~wftliiig'~igr~tions''I~'witIt increased dammi~g arid di-
<br />1"versioIlof'thltsheams, the huriipback suckers apparently declined
<br />greatly in numbers, but the species seems to be readjusting itself to
<br />life in thc modified waters (Wallis, 1951, p. 89; Douglas, 1952;
<br />
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