156 FISHES OF WESTERN SOUTH AMERICA 
| Taczanowskil Taczanowsku 
Characters Rivulatum | Oroyae type from Rio Tingo Atochae 
Head in length |4.5-5.5* | 5.75-6.0 | 4.75-6.5* [4.65.3 | 4.76.3 
Dorsal | 13* ae a0 i 8-9 fleshy 
i Le ie -_ \i011* | 7 73 6-7 fleshy 
Pectoral Vs fie Iso =—ti(iéidrt SQ 
Nasal barbell in | toend of eye iow i 25-1.4 | 1 3 mad 2 9-2 ..6 
head 
Wvaeiitars: 2 - Be ee - none reaching a .21-1 5 1 re a 1 8-2. 0 
barbel same opercle gill-opening 
Mental barbel a _ 1.6-2.0 | f 6t 2. 1 2.40 
same 
Caudal founded il roundeae” - eaesente subtnincate . Pant 
Denk in feneen (arses . “5.75-8.0 7 6.3-8.4 6.0-7.0 8.3-9.8 - 
Dorsal to anal overlaps half overlaps some- barely reaches* barely reaches* overlaps — half 
way what way 
Accessory rays  distinet* few and in- few and in- few, not dis- | Moderately 
_ numerous distinct distinct tinct numerous 
In the above brief tabular analysis, certain characters have attained their 
highest development in one or more species studied. P. rivulatwm has or shares 
the extreme position in six cases, oroyae four times, the taczanowskii types three 
cases, the taczanowskii specimens from the Tingo four times, and atochae eight times. 
Intermediate positions are held by rivulatwm three times, oroyae seven, taczanowskii 
types seven, taczanowskii from the Tingo eight times, and atochae only three times. 
Atochae shares no characters as listed with révulatum, but does so once with oroyae 
and twice with taczanowskii. Thus the characters of the above species seem to 
arrange themselves in a series, following the order in which they are given, rivu- 
latum the most extreme in robustness and in number of finrays, etc., with atochae 
its opposite. (One extreme shown by * ; opposite extreme by italics). 
116. Pyeiprum aTocHAE Allen, sp. nov. 
Plate XIII; figs. 3-5 
17819, many, type and paratypes, 38-105 mm., Rio de Atocha, Atocha, Bolivia, Allen, February, 
1919. 
Allied to Pygidium taczanowskii, oroyae, and rivulatum, in that order, differing 
most strikingly in its slender form and short barbels; middle of eye in advance of 
middle of head; body less compressed midway; caudal peduncle distinctly more 
elongate, about 3.7 in the total length; more distinct lateral band in fresh material. 
Head in total length 6.2; width of head in length 6.4—6.7; width of mouth in 
