CATFISH GENUS NOTURUS RAFINESQUE 13 



of the system varies with the species, usually having seven openings ; 

 there are six in each of four species. A further lateral shift of the 

 anterior pores takes place in Ictalurus so that anterior to the outer 

 mental barbel there are at most only four pores, in some forms three 

 or even two. This shift leaves six to eight pores posterior to the 

 outer mental barbel, as there are typically ten outlets from the canal 

 (not eight or nine as reported in the literature). 



Posterior to the outer mental barbel, six to eight pores from the 

 preoperculomandibular system open below the lower jaw and over 

 the opercle. The most posterior of these emerges at about the middle 

 of the upper edge of the opercle and the next to the last typically 

 opens over the midopercle, directly anterior to the pectoral fin. In 

 Prietella, however, the last two pores are nearer the upper edge of the 

 opercle, while the ninth pore is approximately in front of the pectoral 

 spine. In this species the canal is interrupted between the most pos- 

 terior pores. These adjacent pores probably result from the division 

 of one pore; consequently, although Prietella now normally has 

 eleven pores, it likely has been derived from a ten-pored ancestor. 



The infraorbital canal is rather simple. Anteriorly, it opens by a 

 pore (Ll) posterior to or mediad of the anterior naris. The next 

 pore (L2) opens lateral to these and above the maxilla. Posteriorly 

 there are typically five (six in Prietella and one of two specimens of 

 Trogloglanis has six) other openings along its course before it joins 

 the supraorbital canal to form the lateral canal. The entire canal in 

 Prietella typically has eight pores, the last two being isolated by 

 interruption of the canal from the anterior section. Here again, prob- 

 able disruption of the canal at a pore resulted in an extra pore. An- 

 teriorly the canal passes through the first suborbital, also called the 

 lacrymal bone, hence the symbolic terminology used for the first 

 two pores. Posteriorly, the canal is supported by simple tubes of bone 

 and all other pores arise from centers between these. In passing about 

 the eye posteriorly, the canal swings almost directly upward in 

 Ictalurus, Trogloglanis, Prietella, and Noturus; in Pylodictis and 

 Satan the canal passes diagonally backward. It joins the supraorbital 

 and lateral canals in the frontal. 



The supraorbital and lateral cephalic canals form a simple straight 

 tube which contains five pores. There is no connection between the 

 two sides of the head. Of the pores, the first three exit from the tube 

 traversing the nasal bone and the posterior two from the frontal. In 

 Pylodictis, the anteriormost of the nasal pores (Nl) is relatively small 

 and far ahead of the anterior naris, near the upper lip, and the second 

 (N2) or midnasal pore opens mediad or anterior to that structure. 

 The anterior nasal pore (Nl) in Satan is about midway between the 

 edge of the upper lip and the naris; in the other genera of the family 



