800 ON NEW LORICARIID FISHES. [Nov. 12, 



A single specimen, 110 mm. in total length, collected by 

 Mr. Palmer. 



This species is allied to A, longifilis Stdr., from Peru, which is 

 known to me only from Steindachner's description and figures, 

 but which is separated at least by the smaller mouth, longer 

 caudal peduncle, and different coloration. The teeth in the upper 

 jaw in A. Jieterodon approximate in form to the incisor-like teeth 

 of Arges peruanus and A. simonsii. 



Arges retropinna, sp. n. (Plate XLVIII. fig. 2.) 



Lensjth of head 3 i to "ih in the length of the fish. Interocular 

 width less than the distance from eye to posterior nostril, 

 nearly 4 in the length of head. "Width of mouth a little more 

 than 5 the length of head ; outer series of teeth of the prsemaxil- 

 laries unicuspid, acute ; mandibulary teeth bicuspid ; barbel 

 extending not more than | of the distance from its base to the 

 gill-opening. Dorsal I 6 ; first ray not produced, h, or a little 

 more than ^ the length of head; adipose fin with a well- 

 developed movable spine, which is inserted at a distance from the 

 caudal equal to | the length of the middle rays of the latter. 

 Pectoral spine not produced, but extending to middle of ventral ; 

 ventrals originating well in advance of the doi-sal, not reaching 

 the vent, which is situated at 4 of the distance from base of 

 ventral to origin of anal. Anal I 6. Distance from tip of snout 

 to origin of dorsal 21 to 2\ in the length of the fish, from base of 

 last ray of anal to that of the caudal 7|. Greyish, clouded with 

 darker and with some small pale spots ; dorsal, anal, and pectoral 

 with a series of dark spots ; pectoral dark at the base ; caudal 

 blackish at the base and also posteriorly. 



Rah. Jimenez, Western Colombia. 



Two specimens ( $ ), 55 and 65 mm. in total length, collected 

 by Mr. Palmer. 



This species is allied to A. homodon Rgn. and^. boidengeri Rgn., 

 but is easily distinguished by the smaller and more posteriorly 

 placed dorsal fin, shorter barbels, shorter caudal peduncle, &,c. 



EXPLANATION OF THE PLATES. 



Plate XLVII. 



Fig. 1. Plecostomus ilieringii. 



2. Plecostomus niargaritifer. 



PlATE XLVIII. 



Fig. 1. Plecostomtis strigaticeps. 



2. Arges retropinna. 2 a. Head seen from above. 2 b. Head 

 seen from below. 2 c. Teeth. 



Plate XLIX. 



Fig. 1. Plecostomus alhopunctatus. 



2. Arges Jieterodon. 2 a. Head seen from below. 2 b. Teeth. 



