20 
Indiana University Studies 
plates. Along the dorsal plates the chromatophores spread out 
more or less evenly. Along the ventral plates the chromato- 
phores just below the dots spread out and then narrow to 
form a vertical stripe located either on the posterior edge or 
the middle of the plate. The vertical stripes decrease in 
length posteriorly so that a dark stripe decreasing in width 
backwards is formed. 
Very closely related to Cory dor as natter eri. 
Corydoras aeneus (Gill). 
17235, 42, 43-60 mm., Rurrenabaque. Nov., 1921. 
Family Loricarihle. 
Subfamily PLECOSTOMIN^E. 
Plecostomus plecostomus (Linnaeus). 
17013, 9, 68-212 mm., Lake Rogoagua. Nov., 1921. 
Plecostomus popoi Pearson, sp. nov. Plate III, figs. 2 and 3. 
17010, 4, the largest the type, 32-104 mm., Popoi River, Upper Beni, 
Bolivia. Sept., 1921. 
Head 3.25 ; depth 6.1 ; D. 1,7 ; A. 1, 4 ; the breadth of the head 
1.2 times its length, the depth 2.1 times, the snout 2 times, 
the interorbital 3 times, the eye 7 times; the mandibular 
ramus 3 times in the interorbital ; the supraorbital edges 
slightly raised; the supraoccipital with a low broad median 
ridge; the tip of the snout with a small naked area; the maxil- 
lary barbel not reaching the gill opening by a distance equal 
to the diameter of the eye; maxillary and mandibular bones 
each with 15 teeth; the teeth curved inward at the tips; all 
teeth notched, the outer point turned laterally, the inner 
straight; the dorsal region behind the insertion of the pec- 
torals regularly rounded ; the scutes spinulose, none strongly 
carinate, the first 4 back of the insertion of the pectoral spine 
weakly carinate, 29 in a lateral series, 9 between the dorsal 
and the adipose, 12 between the anal and the caudal ; supraoc- 
cipital margined posteriorly by a median scute and 2 on each 
side; lower surface of the head and abdomen covered with 
small spinulose plates ; the tips of the pectoral spines reaching 
to the base of the ventrals; the ventrals not quite reaching 
anal ; the longest anal ray reaching to the middle of the fifth 
scute back of the base when depressed; the first dorsal ray 
