26 CALIFORNIA ACADEMY OF SCIENCES 



sides and belly, almost entirely masking the silvery of those parts. In other speci- 

 mens, the sides and belly are bright silvery without brown tinge. The fins are all 

 dusky, in some specimens much darker than in others; the ventrals sometimes nar- 

 rowly edged with bright white. 



We have been tempted to consider this species the male of G. dasycejthalus, 

 as our numerous specimens seem to be all males, while our specimens of G. dasy- 

 cephahfs, as well as all those of which we have record, seem to be females. The 

 structural differences are so much greater in amount than are known to be sexual 

 with any other species, that we hold the two forms distinct. In addition to the striking 

 diilerenee in the length and sculpturing of the head, G. longicephalus has shorter 

 barbels, coarser gill-rakers, shorter pectoral spines, a wider fontanel, and a wider 

 snout and mouth. 



38. Sciadeichthys troscheli (Gill). 



Abundant along the entire coast of Mexico and Central America. At 

 Panama it occurred daily in the markets, but seldom in large numbers. The collec- 

 tion contains five specimens from Panama, one from Champerico. 



The species varies in certain respects more than has been represented. The 

 dorsal buckler varies much in width, and even in general shape; one specimen at 

 hand has it triangular, tapering nearly uniformly from the base forward to the long 

 acute apex, two-fifths of its length on the median line being contained within the 

 notch of the occipital process. In one individual, the granulations are very sparse, 

 and largely obscured by the thickened integument. 



The maxillary barbels are blackish, with a consjiicuous white inferior mar- 

 gin. They vary much in length, often failing to reach opercular opening, sometimes 

 overlapping base of pectoral spine. The vomerine patch of teeth is sometimes long 

 (transversely) and narrow, thus separating widely the palatine bands (as figured by 

 Eigenmann and Eigenmann, 1890, p. 56); sometimes much shorter and wider. The 

 head seems very constant in length, 3i to 3i in total length (without caudal). 



39. Selenaspis dowi (Gill). 



Large specimens are frequently brought into the Panama market, but seldom 

 more than two or three at a time. The young are rarely seen. In one of the speci- 

 mens at hand, a curious variation is observable in the shape of the dorsal shield, which 

 has its anterior margin medially produced and wedge-shaped, fitting into an 

 emargination in the occipital process, much as in Sciadeichthys troscheli 



40. Netuma kessleri (Sieindachner) . 



One of the most abundant species of catfishes at Panama. It varies in color 

 from light brown to nearly black on the upper parts, and may be pure white below 

 or variously marked with brown. The fins vary in a similar manner, the caudal, anal, 

 and inner surfaces of pectorals and ventrals being black in the darkest specimens, 



