12 U.S. NATIONAL MUSEUM BULLETIN 2 82 



information on several forms; and brief descriptions of the system have 

 appeared in anatomical discussions of certain species. In this study of 

 the Ictaluridae, reference has been to R. R. Wright (1884b), Herrick 

 (1901, pp. 23(M231), and Kindred (1919). On certain details of struc- 

 ture their findings are not in agreement with my data. 



In this family the canals are simple tubes. At intervals along their 

 course these give off short lateral branches that extend to the surface 

 and open through pores. The canal system is either imbedded in the 

 large bones or retains cylinders or ringlets of bone (see also McMurrich, 

 1884, p. 279) for support. The ossified ringlets probably continue 

 posteriorly to the end of the functional lateral line in the Ictaluridae. 

 Stained specimens show that the infraorbital canal and short sections 

 of the canals extending between the large bones are enclosed in these 

 ringlets. Those stained without removing the skin exhibit the ringlets 

 along the side of the body, where they extend to the end of the lateral 

 line. 



The canal system consists of the preoperculomandibular canal, 

 the infraorbital canal, the supraorbital canal, the lateral cephalic 

 canal, and the lateral body (line) canal (pi. 1). In disagreement mth 

 R. R. Wright (1884b, pp. 264-265), I count more pores in the pre- 

 operculomandibular canal and find that this tube is not isolated but 

 connects with the lateral cephalic canal; however, in Prietella only a 

 short section connects with the lateral canal as the preoperculo- 

 mandibular canal is interrupted. Also I find no evidence of an occipital 

 commissure. 



The preoperculomandibular system traverses the lower jaw and 

 preopercular bones, usually connecting with the lateral cephalic 

 canal by one or more short ossified tubules or ringlets. Along its course 

 it opens to the outside from 10, 11, or 12 pores, the number depending 

 upon the species (tables 1 and 22). Of these pores, the first two to 

 five open below the lower jaw in front of the mental barbels. In 

 Pylodictis and Satan the first pore is median and a common outlet 

 for the preoperculomandibular canals of both sides of the head. In 

 other genera, the distance between the anterior pores is considerably 

 greater, varying from a moderate separation in Noturus, Prietella, 

 Trogloglanis, and in certain species of Ictalurus to a rather wide 

 separation in other forms of Ictalurus. 



Variations in number of pores in the preoperculomandibular canal 

 seem to be of considerable significance, but the relative spacing is in 

 part an expression of the development of the encasing dermal bones. 

 The canal in Pylodictis and Satan has five pores (counting the median 

 pore) in front of the posterior base of the outer mental barbel and 

 seven posterior to that element. In Noturus, Prietella, and Trogloglanis 

 there are usually only four anterior pores, but the posterior portion 



