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yA
<br />172 Bailey and Cross
<br />Huso, constitute the Acipenserinae. On the basis of the comparison
<br />given by Forbes and Richardson (1905: 41) we were uncertain
<br />whether the two genera of "shovelnose" sturgeons (.Scaphi,•)1 I'll
<br />:: ;s
<br />and Pseudoscaphirhynchus) owed their close resemblance to co►nmor,
<br />ancestry or to convergence. Examination of three specimens of P,
<br />kaufmanni1 and perusal of a translation of the acipenserid section of
<br />Berg's-freshwater fishes of Russia (1932: 42 -70) leads us to believe
<br />that Berg's arrangement is correct, namely, that the genera of the
<br />Scaphirhynehinae are directly related. However, it is perhar,s pre-
<br />mature to deny categorically that the striking agreement :n ..,•,,al
<br />features may be due to parallel modifications in animals that inhabit
<br />the 'channels of large silty rivers. Scaphirhynchus is much more
<br />highly specialized from the ancestral stock, exemplified presumably
<br />by _-lcipnnser, than is Pmudoscaphirhynchus.
<br />The apparent relationships and chief differential characters may
<br />be expressed in the following key to the Recent genera of u,
<br />KEY TO SUBF_A-MMIES A \D GENERA
<br />Ia. AcIPE sERPiAE. Spiracle and pseudobranchium present. Snout variously
<br />blunt or sharp, more or less conical, never extremely depressed and shovel-
<br />like. i'pper lobe of caudal not prolonged into a filament.
<br />4a. Gill membranes fused to isthmus, not forming a free fold below it. !r. , h
<br />transverse, of moderate size, much narrower than rostrum. Barbels sub -
<br />circular in cross section. North .America and Eurasia. Approxic:,. _iv
<br />fourteen species .......................... ........ I ..... ... Acipenser
<br />?b. G;;. ;membranes conjoined, forming a free fold below the isthmus. Mouth
<br />crescentic, large, nearly as wide as rostrum. Barbels flattened. Eur-
<br />asia: drainage of the Amur Ricer, eastern Siberia, and basins of the Cas-
<br />pian, Black, and Adriatic seas. Two species. ................ Huso
<br />1b. SC. ,.PHIRHY\cHm.jE. No spiracle or pseudobranchium. Snout extremely
<br />depressed, broad and shovel -like. Upper lobe of caudal often t-. r•: 1,
<br />but the filament said to be wanting in Pseudoseaphirhynchus 1;. ., ..,...
<br />and may be lost through mutilation.
<br />3a. Caudal peduncle incompletely armored, little depressed, and short —tip
<br />of anal fin reaching almost to caudal base; caudal- peduncle length
<br />about 9 per cent of standard length. Barbels entire. Gill openings
<br />with their lower ends (where they join the isthmus) separated by a
<br />space of about one third the rostral width. Pectoral spine very stout.
<br />Each clavicle with a deep ventral keel that has from d to 5 strong,
<br />' US \_ll 37444, 143 mm., Amu Darya River, $iberia; liSNNI 102346, 143 mm.,
<br />Tchardjuy, U.S.S.R., June I4, 1916; DSNM 104347, 337 mm., mouth of Amu Darya
<br />River, Siberia, September 4, 1945.
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