158 BULLETIN 150, UNITED STATES NATIONAL MUSEUM 



species. The number of rays, the extent of the pectoral notch and 

 development of the middle pectoral rays, the length of the lower 

 pectoral lobe, and the level at which the upper edge of the pectoral 

 is attached to the body have been found to be of the most importance. 



The pectoral notch is distinct in all the species except P. fimbriatuSy 

 in which it is hardly evident. P. fimbriatus is distinguished also by 

 the pectoral rays being evenly spaced on the girdle. The middle 

 pectoral rays are, in all the other deep-sea species of the family, more 

 widely spaced than the rays above or below. In species like P. 

 Tiolomelas and P. hathyhius in which the pectoral notch extends to or 

 nearly to the girdle the middle rays are reduced to short filaments 

 and may not project into the fin membrane. In none of the species 

 examined by the writer, with the possible exception of P. rosaceus, 

 in which one ray appears to have been torn away, is the middle of the 

 girdle bare of rays for an unusual distance. The distance between 

 the rudimentary rays may progressively increase toward the lower 

 lobe. The space between the lowest rudimentary ray and the upper 

 ray of the lower lobe was never found to greatly exceed the space 

 between the two lower rudimentary rays. Giinther describes P. 

 hathyhius and Gilchrist P. australis as having the girdle opposite the 

 notch free of rays. 



The length of the lower pectoral lobe varies considerably. In 

 P. melanohranchus the lower lobe is contained twice in the head and 

 in P. mento it is longer than the head. The variation of the length of 

 the lobe within the species can not be studied because of the lack of 

 material. 



The lower pectoral lobe never consists of graduated rays as in 

 Careproctus and Liparis. In some of the species the lower ray is not 

 more than one-half the length of the next ray but there is never a 

 series of rays beginning with a short one and increasing regularly in 

 length. 



The rays of the lower pectoral lobe are usually half free. In some 

 species, as in P. liolomelas , they are free practically to the base. They 

 are frequently coiled or wavy at the tips. 



The level on the side of the body at which the upper part of the 

 pectoral fin is fastened is considerably lower in some of the species 

 than in others. In the more generalized species the upper edge of the 

 pectoral is on a level with the pupil. In P. cepTialus it is below the 

 level of the orbit and in P. mento below the angle of the mouth. In 

 these species the pectoral girdle becomes more oblique and the 

 symphyses of the pectoral is carried forward onto the throat until, as 

 in P. mento, it is in front of a vertical from the anterior border of the 

 eye. Associated with the lowering of the pectoral is the projection 

 and enlargement of the lower jaw and the changing of the angle of the 

 mouth. 



