NO. 3538 CHARACID FISHES — WEITZMAN 41 



to British Guiana. All the aquarium specimens that I have seen 

 over the past 10 years have had approximately the same color pattern. 

 Thus it appears that aquarium fish collectors are collecting all their 

 specimens from the same general area. Very probably this is from 

 the vicinity of Georgetown in tributaries of the Demerara River, 

 British Guiana, where the fishes are known to occur and where col- 

 lectors are known to have been active in the last several years. In 

 many respects, the color and breeding habits of Poecilobrycon harrisoni 

 are like those of Nannostomus bectfordi suggesting that the two may 

 have been derived from a common ancestor and may be related more 

 closely than their morphology indicates. 



The type of Archicheir minutus is the young of Poecilobrycon 

 harrisoni. The type was studied at the Chicago Natural History 

 Museum and found identical mth young specimens of harrisoni 

 spawned and raised in the author's aquarium. 



Specimens examined. — Two, paratypes, CAS(IUM) 11709, SL 36.5-41.5 mm., 

 British Guiana, Canal at Christian burg, Demerara River, 1908, C. H. Eigen- 

 mann.— Four, SU 50243, SL 34.0-38.0 mm., British Guiana, Georgetown.— 

 Twelve, SU 50245 (one alizarin preparation), SL 31.0-37.5 mm., British Guiana, 

 no other data. — Three, SU 50244, SL 13.3-44.5 mm., aquarium specimens, 

 Aug. 21, 1956, S. H. Weitzman.— Eight, SU 50246, SL 9.5-37.5 mm., aquarium 

 specimens from Demerara River, British Guiana, and their young aquarium 

 spawned and raised, S. H. Weitzman. — Seven, SU 50446, SL 17.0-44.5 mm., 

 British Guiana, Atkinson Field Creek, near Hyde Park, tributary of the Demerara 

 River, Nov. 11, 1957, Rosemary Lowe (McConnell). 



Subgenus Nannobrycon Hoedeman 



Diagnosis. — Rays of caudal fin arranged unlike those of all other 

 nannostominans; 10 rays of upper 4 hypural plates not all entering 

 upper caudal lobe. Lowermost 2 of these rays enter lower caudal 

 lobe, giving that lobe greater depth than upper lobe. Lower caudal 

 lobe usually with dark pigment extending w^eU onto fin, sometimes 

 over its entire surface. Normal resting position of living members of 

 this subgenus oblique, snout upwards. Angle of this oblique position 

 is from about 45° to about 75° or 80°. 



Remarks. — 'Hoedeman (1950) proposed Nannobrycon as a generic 

 name for Poecilobrycon eques (Steindachner). In it he included only 

 this species, believing P. unifasciatus to be a synonym of P. eques. 

 Both species of this subgenus have the same peculiar caudal fin 

 structure and behavior mentioned above. Hoedeman (1950) noted 

 that the shape of the swim bladder of the members of this subgenus is 

 different from those of aU other nannostominans that he examined. 

 However, he did not examine the swim bladder of Poecilobrycon 

 harrisoni, as he had no specimens. The swdm bladder differences that 

 Hoedeman noted were crudely presented and are not suitable to 

 distinguish harrisoni from eques and unifasciatus. However, the 

 219-936 — ee 



