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<br />2~4
<br />
<br />Hubbs and Miller
<br />
<br />Hybridization between Catostomus and Xyrauchen
<br />
<br />~~5
<br />
<br />* Distance from front of upper lip to line joining posterior tips of toi,es of low:r
<br />lip.
<br />
<br />t :,east di.stance ?etween papillae at extreme base of lobes of lower lip, but dis-
<br />regardmg papIllae at Isthmus that clearly arise between the lobes.
<br />
<br />with X. texanus, probably because they are relatively large on the
<br />average and the eye decreases rapidly in proportional size with age.
<br />For some reason that is not obvious, the lips of the hybrids average
<br />even lower in proportional size than those of X. texanus. In the
<br />two dorsal-fin measurements and in the distance between the pectoral
<br />fins the intermediacy is striking.
<br />Five sets of measurements used in checking the intermediacy of the
<br />Catostomus latipinnis X Xyrauchen texanus hybrids were found to
<br />be inapplicable to the C. insignis X X. texanU8 analysis, because the
<br />values for the parental species overlap very widely and the dif-
<br />ferences between the means is less than 5 per cent. Four sets of
<br />measurements that were not applicable to the C. latipinnis X X.
<br />texanus analysis were found useable in the present comparison.
<br />In this combination the intermediacy in scale structure can
<br />hardly be said to apply to the general shape of the scale, which is not
<br />strikingly different in Catostomus insignis and Xyrauchen texanus,
<br />but it does apply to the greater tendency for radii to develop on the
<br />lateral field in C. insignis and applies particularly to the number of
<br />basal and apical radii, which are most numerous in C. insignis, in-
<br />termecliate in the hybrids, and fewest in the young ofX. texanus.
<br />The differences in scale imbrication, and in gill raker structure, are not
<br />striking in the young specimens.
<br />Though the nuchal keel is still developing in the young of Xyr-
<br />auchen, the intermediacy of the hybrids is clear-cut in this charac-
<br />ter. Catostomus insignis has no trace of the keel. In the hybrids it
<br />is definitely evident, but is less elevated, less firm, less trenchant,
<br />and more evenly curved anteriorly than in the young of X. texanus.
<br />X-ray photographs reveal, under microscopic examination, the inter-
<br />mediacy of the supporting structural elements of the nuchal hump,
<br />just as they did for the C. latipinnis X X. texanus hybrids (PI. III).
<br />As indicated by radiographs of two of the hybrids, these structures
<br />are more expanded than in C. insignis but are conspicuously less
<br />developed than in X. texanus.
<br />In this combination as in the other, the hybridity of the aberrant
<br />specimens is especially obvious in lip characters (PI. IV). Except
<br />that the lips do not become so excessively elongate in Catostomus
<br />insignis as they do in C. latipinnis, the basic differences in lip
<br />structures are similar in the two hybrid combinations and, in both,
<br />the hybrids are strikingly intermediate.
<br />
<br />st01;t~s insignis in this series was small enough, we utilized also six
<br />s~el~lmens (U.M.M.Z., No. 131118) from the same stream, Tonto
<br />CrEek, coll:cted abo,:,e Gisela, and four (U.M.M.Z., No.131106)
<br />frOln Salt RIver one mIle above the head of Roosevelt Lake to h' h
<br />1, t C k' 'b ' w IC
<br />on 0 ree IS tn utary.
<br />
<br />TABLE VII
<br />
<br />PROPORTIONAL M1GASUREMENTS OF CATOSTOMUS INSIGNIS, HYBRIDS, AND
<br />XYHAUCHEN TEXANUS
<br />. 'The ~easurements are expressed as thousandths of the standard length. The
<br />IIp ald glllraker measurements were made by Hubbs, all others by Miller. We 1'01-
<br />lowe~l. the ~ethod.s recommended by Hubbs and Lagler (1947, pp. 13-15, figs. l!-5).
<br />Precl~IOn ~lal cahpers were used in measuring the smaller parts, under adequate
<br />magI clficatIOn.
<br />
<br />- --- ---
<br />~--~~
<br /> C.insignis Hybrids X. texanus
<br /> Measurement (11 specimens) (6 specimens) (13 specimens)
<br /> Range ;\Jean Range Mean Range Mean
<br />.----".- ------
<br />Standard length, in mm. --.--
<br />52.(;-70.0 66.1 53.7-77.7 71.3 57.8-76.7 6l!.1
<br />CaudIl-peduncle depth 81-107 100 93-99 97 76-91 85
<br />Snoui length. . . . . . . . . . 120-131 124 107-116 Ill! 99-113 107
<br />Eye diameter.. . . . . . . . 56-70 61 51-63 56 50-61 56
<br />Lips, overall length * .. . ! 57-76 68 46-63 54 49-61 56
<br />Separ:ltion, lower lipst . ' 1.2-4.1 2.7 3.3-12.0 6.8 4.6-10.6 8.0
<br />DorsEtl fin, depressed
<br />lenfth . . . . . . . . . . . . . 294-318 304 304-344 325 336-361 348
<br />Dorsa I fin, length of
<br />has" . . . . . . . . . . " . . . 205-225 215 l!13-259 l!35 244-274 l!61
<br />Interpeetoral space . . . . 98-118 [109 82-108 97 74-100 89
<br />
<br />In the least. de.pt~ of the caudal peduncle the approach is closer'
<br />to Catosto:nus mstgms, partly because the range and the mean for
<br />that specIes are lowered by one abnormally slender pedunele meas-
<br />urement. In snout length the approach is closer to x"yrauchen
<br />te~an us, per?aps because the hybrids have the largest aver'age and
<br />tlus I;roportlOn decreases with age. In eye length the hybrids agree
<br />
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