218 U.S. NATIONAL MUSEUM BULLETIN 2 82 



Other characteristics that are interpreted as speciaHzations include: 

 the formation of a free posterior flap or shortening of the base of the 

 adipose fin (with increase in size as well as with specialization) ; 

 degeneration or loss of skeletal parts; reduction of the number of 

 hypurals and their fusion distally; development of posterior serrae on 

 the dorsal spine in Ictalurus; fusion of the two ossified pectoral radials ; 

 extreme development of chewing surfaces, especially those of the pre- 

 maxilla from a short, rectangular patch; backward elongation of the 

 supraoccipital process; a greatly depressed or a highly arched skull; 

 a short or an extremely long anal fin ; a few or many rayed caudal fin ; 

 perhaps an included lower jaw; loss of eyes and pigmentation; probably 

 an increase in the number of preoperculomandibular pores ; the anterior 

 union of the sensory canals, especially that of the infraorbital and 

 supraorbital canals, in some Noturus and Satan, and that of the pre- 

 operculomandibular canals in Satan and Pylodictis; excessive elonga- 

 tion or shortening of the posterior process of the cleithrum; and the 

 shortening of, addition of a posterior chamber to, or loss of the air 

 bladder. 



The total number of caudal rays in Ictalurus and Pylodictis is un- 

 known, but they typically have 15 branched rays. In Noturus, the 

 range of variation of the total caudal ray count is 39 to 67, and the 

 average of the means for the species is 53.2. The limited available data 

 on Ictalurus and Pylodictis indicate that they too have approximately 

 50 caudal rays. This is perhaps close to the primitive condition. If so, 

 divergence may be regarded as a specialization. 



The fossil history of the Ictaluridae is little known. Spines and other 

 elements from Ictalurus, resembling those of modern bullheads, are 

 known from Lower Pliocene deposits. Also, spines of one close to, if not 

 identical to, Ictalurus furcatus have been reported (Hubbs and Kibbard, 

 1951) from the Lower Pliocene. Elements that seem identical with the 

 recent Ictalurus punctatus and Pylodictis olivaris are known from 

 Pleistocene deposits, but fossil representatives of Noturus and the blind 

 species are unknown. This absence of fossil Noturus is undoubtedly 

 due to the nature of the habitat in which they lived. Spines of catfish 

 resembhng bullheads are common fossils, but since many Noturus 

 occupy riffle habitats or regions of erosion, rather than of deposition 

 as do several of the bullheads, their fossilization is unlikely. Noturus 

 gyrinus and others living in lowland streams or lacustrine waters where 

 the chance of fossilization is greater are most likely to be found as 

 fossils. 



Despite the poor fossil evidence, it seems plausible to assume that 

 the family arose early, perhaps early in the Tertiary or late in the 

 Cretaceous; that the genera had an early origin; that Ictalurus and 

 Noturus have had a long history; and that the group represented by 



