CATFISH GENUS NOTURUS RAFINESQUE 15 



rectangular patch. Its width and lateral edges are rather variable, 

 and various posterior extensions of the patch may invade the rear 

 surface of the premaxilla which is variously extended backward. The 

 variable posterior extension may be short and scarcely evident, mod- 

 erate and from the posterior edge of the premaxilla {Ictalurus halsanus), 

 long, narrow, and from near the posterior corner {Noturus jlavus; 

 pi. 2, fig. 3), or broad, long, and from the posterior edge (Pylodictis 

 olivaris) . 



The shape of the caudal fin varies from species to species. Variations 

 in the posterior fin margin are: rounded to deeply forked in Ictalurus; 

 slightly emarginate in Prietella, Trogloglanis, and Satan; truncate or 

 rounded to pointed in Noturus; and emarginate to rounded in Pylo- 

 dictis. The degree of development and shape of serrae on the spines 

 varies greatly throughout the species of catfishes. The skeleton is well 

 ossified and the bones are heavy in species that attain a large or rela- 

 tively large size, particularly Pylodictis olivaris, Noturus Jlavus, and the 

 forms of Ictalurus. The bones are somewhat thinner in small species. 



The ectopterygoid, broad in both Ictalurus and Pylodictis, is some- 

 what reduced in breadth in Prietella and is narrow in the species of 

 Noturus. Similarly, the post-temporal bone is present in Ictalurus and 

 Pylodictis, but is absent or vestigial in both Prietella and Noturus. 

 Since the bones of both Satan eurystomus and Trogloglanis pattersoni 

 are thin, both of these elements (not examined) could be expected to be 

 reduced. The width of the opercle varies considerably; it is broad in 

 most forms, but narrow in Noturus. The bone is relatively little nar- 

 rowed in Prietella. 



One epural is typically present in most species, but occasional speci- 

 mens have two. Both Pylodictis and Ictalurus appear to have seven 

 hypurals, with only infrequent reduction to six. Of these, three (1-3) 

 support the lower lobe of the caudal fin and four (4-7) support the 

 upper lobe. Three species of Noturus, subgenus SchUbeodes, possess a 

 modal number of seven (1-3 + 4-7) hypurals. All others normally 

 have six (1-3 + 4-6). Fusion of the hypurals in the specimens of 

 Prietella studied prevents their enumeration. 



The variation in branchiostegal rays in the family is 8 to 13. Two 

 branchiostegals are typically associated with the epihyal; a third is 

 sometimes at the junction of the epihyal and ceratohyal so that it 

 could be included in the count for the epihyal; all other branchiostegals 

 are associated with the ceratohyal. Pylodictis is the only species that 

 normally has twelve branchiostegals. Two specimens of Satan have 

 eleven, but the type-specimen has ten. In Noturus and Prietella, the 

 variation is eight to twelve with modes from nine to eleven. The limited 

 data from Ictalurus and Trogloglanis indicate a range of eight to eleven 

 branchiostegal rays with modes eight to ten. 



