ANNOTATED LIST OF THE SPECIES 185 
Hypostomus guacari Lacépede, 1803, Hist. Nat. Poiss., 145. 
Plecostomus guacari Regan, 1904, Trans. Zool. Soe. London, XVII, 205. 
Both slopes of Panama and southward to Uruguay 
167. Hyposromus PHRIXOSOMA (Fowler) 
Plecostomus phrixosoma Fowler, 1939 (1940), Proc. Acad. Nat. Sci. Phila., XCI, 233, figs. 21-23, 
one, type, 150 mm., Contamana. 
Known from the type taken at Contamana 
Near H. commersonvi and punctatus Cuvier and Valenciennes. The common 
name Carocha de brada was supplied to the collectors. 
Genus 75: HEMIANCISTRUS Bleeker 
Hypostomus (in part) Cuvier and Valenciennes, 1840, Hist. Nat. Poiss., XV, 489, sp. 
Ancistrus Kner, 1853 (1854), Denksch. Kk. Akad. Wiss. Wien, VII, 272; 
Regan (in part), 1904, Trans. Zool. Soe. London, XVII, 221. 
Hemiancistrus Bleeker, 1863, Nederl. Tijdsch. Dierk., I, 78; 
Eigenmann and Eigenmann, 1890, Occ. Papers Cal. Acad. Sei., I, 417; 
Eigenmann, 1910, Rept. Princeton Univ. Exped. Patagonia, III, 408. 
Chaetostomus (in part) Giinther, 1864, Cat. Fish. Brit. Mus., V, 240. 
Type: Ancistrus medians Kner 
La Plata and Amazon systems, Guianas to Panama 
The enclosure of the ventral surface by small plates led to its designation by 
Kner as medians, intermediate between Ancistrus and Plecostomus (Hypostomus) ; 
Bleeker held this character as sufficient justification for the present genus. Sepa- 
rated from the preceding by the erectile spines borne on a movable plate; dorsal 
and adipose fins not approximated; margin of snout granular, sometimes with a 
naked spot near the tip; body deep, plates keeled, occipital keeled; teeth small; 
D. I, 7, the last ray connected with the succeeding scute by a small membrane. 
‘““All species seem to be rare.” 
168. HEMIANCISTRUS UCAYALENSIS Fowler 
Hemiancistrus ucayalensis Fowler, 1939 (1940), Proc. Acad. Nat. Sci. Phila., XCI, 235, figs. 24-25, 
three, type and paratypes, 117-124 mm., Contamana. 
The Ucayali basin, Contamana 
169. HeEMIANCISTRUS ARENARIUS Eigenmann and Allen, sp. nov. 
Plate VI, fig. 2 
15356, 2, 94 and 106 mm., the latter the type, Yurimaguas, Allen, November, 1920. 
15357, 1, 123 mm., Alto Maranon, below Pastaza, Allen, October, 1920. 
15358, 1, 129 mm., Amazon, Iquitos, Allen, September, 1920. 
Head 2.66-2.9; depth 4.0-4.33; D. I, 7; A. I, 4; scutes 24 + 1; width of head 
1.2 in its length; interorbital 2; eye 6, 3.5 in the snout; longest interopercular spine 
