8 U.S. NATIONAL MUSEUM BULLETEST 282 



Sensory canal system. — Variation was found in the number of 

 pores in the preoperculomandibular canal and in the region of the 

 anterior naris. Counts of both sides are tabulated individually. The 

 internasal pores are the openings in the area between the anterior 

 naris and the nasal barbel. If the count is given as one, the infraorbital 

 and supraorbital canals are interpreted as fused anteriorly (pi. 1, fig. 

 1); if two, the canals are apparently not connected in this region 

 (pi. 1, fig. 2). The variant count of three indicates the unfused condi- 

 tion and an extra pore mediad to the supraorbital canal. If the most 

 anterior preoperculomandibular pore is common to both sides, it is 

 included in both counts (as in Pylodictis). 



Branchiostegal rays. — Counts of both sides, including all rudi- 

 ments, are tabulated individually. Nearly all are from cleared and 

 stained specimens; otherwise the rays usually cannot be counted 

 accurately. 



Gill rakers. — Counts are of the total number, including rudi- 

 ments, on each anterior gill arch. Ranges given in the descriptions of 

 Noturus are based on five or more specimens. 



Ribs. — Data, from both sides, were taken only from cleared and 

 stained specimens. AU rudiments are included. 



Vertebrae. — Tabulations do not include elements in the vertebral 

 complex (of which there are five fused vertebrae, see p. 31); all other 

 vertebrae, including one terminal vertebra with attached hypurals, 

 were counted. Caudal vertebrae are those beginning with the first 

 hemal arch with a single spine and include the terminal vertebra. 

 Precaudal vertebrae are those anterior to the first vertebra bearing a 

 hemal spine (excepting elements in the vertebral complex). Vertebrae 

 anterior to the origin of the anal fin are the precaudal vertebrae plus 

 those with hemal spines preceding the first pterygiophore of the 

 anal fin. 



Hypurals. — The hypurals are enumerated from below upward. 

 Thus, hypurals 2-3 refers to the second and third hypurals as counted 

 from below. They are frequently fused along their adjoining surfaces, 

 except a broad gap exists between the lower three and the upper 

 three or four. Hypural 1 has a hemal arch and has been termed a 

 (the last) hemal spine in several recent papers. 



Measurements 



The measurements given are mostly self explanatory, and are 

 described, with the exception of the points noted below, in Bailey 

 and Taylor (1950, p. 33); most are in Hubbs and Lagler (1947, pp. 

 13-15). The lengths of dorsal and pectoral spines, barbels, and fins, 

 and the depth of the head become relatively lessened with age; other 

 parts seem to remain quite constant. Ranges of eye size, in the descrip- 

 tions of Noturus, are based on five or more specimens. 



