EEPOKT ON ICHTHYOLOGY. 417 



Teeth subulate and aggregated in a short laterally-truncated Imiid on eai'li jaw. 



Hranchidstcgal rays eight or nine. 



Dorsal fin situated over the interval between tiie pectoral and vcntnd iins, higher 

 than long, with one s])inous and six articulated rays. 



Adipose fin pcduiicnlated and over the posterior portion of the anal. 



Anal fin long, aiid iirdxidcd with twentv-five to thirty or more ravs; it com- 

 mences near the anus. 



Ventral iins provi(h'(l cadi with one simple and seven branchc<l raj's. 



Caudal fin elongated and ipiite deeply forked, Avith the lobes equal and pointed. 



The genus Ictahinis is at (Hice recognized by its forked caudal iin, and its cnm- 

 pre.ssed, elongated, and slender body, which gives to it a peculiarly graceful appear- 

 ance, very unlike that of the stout, oliese, and large-headed catfish of our Eastern and 

 Middle States. The head is smaller in proportion than in the Amluri, more com})ressed, 

 and not covered by so tiiick a skin; the mouth, as we should naturall}' expect, is also 

 very considerably snialler. lint perliaps the most important distinction resides in the 

 mode of insertion of the su|)ra-occipital or interparietal bone into the head of the sec- 

 ond inters})inal. A firm and inunovable bridge is thus formed, and gives an uiunter- 

 rupted passage from the dorsal iin to the snout. 



ICTALURUS SIMPSdNII, Gill. 



The bod}' is slender, elongated, and compressed; the height is greatest at the dorsal 

 fin; it is there ecpial to between a fiftii an<l sixth of the total length from the snout to 

 the concave margin of the caudal; thence it gradually declines fi»r some distance, more 

 raj)idly as it approaches the end of the anal fin, the dorsal and especially the abdominal 

 outlines over the anal iin being slightly ciu-ved. The candid i)eduncle is least high 

 near the middle, where it ecpials a twelfth of the total length. The greatest thickness 

 is at the bases of the pectoral fins, and is about eight-ninths of the height; thence it 

 quite regularly diminishes to the compressed and thin base of the caudal tin. 



The head is conqn-essed, and presents in protile an ol)long-conical form; from tiie 

 projecting snout to the margin of the bony oiiercuhim it forms twentA'-tw o hundredths 

 of the total length, exclusive of the lo))es of the caudal iin. The height, at the vertical 

 of the margin of the operculum, nearly equals a sixth of the total length, and bears the 

 relation to the length of the head of fifteen to twenty-two. The head above is oblong 

 and nearly regularl)- decreases in width from the pectorals to the snout; at the verti- 

 cal of the eyes, it equals tln-ee-(piarters of the greatest widtii, and the bony hiterorbital 

 space only equals three-eighths of the same. The head aliove is transversely arched 

 posteriorly, and beneath is tlat. 



The eyes are large and oval, mostly situati<l in the anterior half of the head on 

 the sides. The largest diameter is between a fifth and sixth of the head's length; the 

 interorbital space is double the diameter. 



The maxilhuy barbels are slender, and extend beyond the opercula. The nasal 

 barlx'ls are very slender, and are scarcel}' longer than the diameter of the eye. The 

 infra-maxiliar\' barbels are in a curved line nearl)- parallel with the jaw; the external 

 53 B u 



