BULLETIN OF THE UNITED STATES FISH COMMISSION. -1 7 



scarcely rugose. Gill-membranes forming a narrow fold across isthmus 

 posteriorly. 



Dorsal spine very high, 1| iu head, a little longer than pectoral spine. 

 Humeral process granular, not quite two-fifths length of pectoral spine. 

 ]STo axillary pore. Adipose fin adnate posteriorly. Caudal long, its 

 upper lobe longest, somewhat falcate, l^V m head. Anal rather high. 



Color brown, with bluish reflections; lower parts dusky, with dark 

 punctulations. Fins all blackish; maxillary and outer mental barbels 



dusky. 



A single male specimen was obtained at Panama. 



SPECIMEN IN UNITED STATES NATIONAL MUSEUM. 



29T76. Panama. Gilbert. 



13. Arius assimiiis Giinther. 



Arius assimiiis Giinther, Cat. Fish. Brit. Mus. v, 146, 1864 (Lake Yzabal); 



Giinther, Fish. Centr. Arner. 1869, 474 ; Steindachner, Fisch-Fauna des Casca 



etc. 1*80, 39 (no description ; Magdalena Eiver, in brackish water). 

 ? Arius seemani Giinther, Cat. Fish. Brit. Mns. v, 147, 1864 (" Central America " : 



specimen with the fontanelle extending to base of occipital process). 

 ? Arius cwrulescens Giinther, Cat. Fish. Brit. Mus. v, 149, 1864 (Huamacbal). 

 Arius guatemaknsis Steind. Icbtb. Beitr. iv, 18, 1875 (Magdalena Bay ; Altata 



Panama). 



Habitat.-- Both coasts of tropical America; Magdalena Bay; Mazat- 

 lan; Altata; Panama; Lake Yzabal (in Guatamala, tributary to Bay of 

 Honduras); Magdalena Kiver (tributary to Caribbean Sea). 



Head 3± (4f in total); width of head 5£; depth 5 (6f); length (28299) 

 11 inches. D. I, 7; A. 4, 14. In the largest specimen (29213) the head 

 is 4 in length. 



Body comparatively elongate, the head depressed but not very broad, 

 somewhat broader than high ; eye rather large, 5 to G in length of head; 

 width of interorbital space 2^ in head; breadth of mouth 1|; length 

 of snout 3£. 



Teeth all villiform ; bauds of vomerine teeth separated by a rather 

 wide interval, each small, roundish, confluent with the neighboring 

 palatine band, the junction marked by a slight constriction ; palatine 

 bands ovate, broad behind, varying considerably in size and somewhat 

 in form, the width ranging from one-third diameter of eye to two-thirds, 

 being generally largest in adults ; band of palatine teeth without back- 

 ward prolongation ; band of premaxillary teeth rather broad and short, 

 its length about o times its breadth. Maxillary barbel reaching a little 

 past base of pectoral in the young, scarcely to gill-opening in the adult ; 

 outer mental barbels 2 in head, inner .3. 



Ante-dorsal shield very short, narrowly crescent-shaped, its length 

 on the median line not more than half that of one of its sides. Occipital 

 process subtriangular, not quite as long as broad at base, with a strong 

 median keel, its edges slightly curved. A short distance in front of 

 the beginning of the keel is the end of the very narrow groove-like 



