NO. 3 BARNARD : THE PHOXOCEPHALIDAE 187 



ftoridanus and P. epistomus (Plate 21, fig. H and Plate 6, fig. K), may 

 be separated on the basis of this length ratio. 



Some species, such as P. variatus, have the sixth articles of the 

 gnathopods quite narrowed and rather slender (Plate 3, fig. G), in 

 contrast to the usually broad, slightly inflated sixth articles of most 

 species. In these cases of narrowed propodi (sixth articles), the palm 

 is usually transverse compared to slightly oblique in the broader propodi. 



Peraeopod 3. — Considerable variation occurs in the width of the 

 fourth and fifth articles of this appendage. At one time Pontharpinia 

 Stebbing 1897 and Parharpinia Stebbing 1899 were distinguished by 

 the stoutness or slenderness of peraeopods 3 and 4. These appendages 

 vary so much from species to species that no qualitative break can 

 now be recognized (Plate 2). 



It is conventional to compare the widths of articles 4 and 5 to the 

 width of article 2, the latter being rather uniformly expanded through- 

 out the genus. Articles 4 and 5 range in breadth from broader than 

 to less than one third as wide as article 2. 



In general, the stouter the appendage the more heavily it is armed 

 with spines and setae, which may indicate that such species are better 

 diggers or burrow in coarser sediments. 



Differences in width between articles 4 and 5 occur from species to 

 species and occasionally may occur intraspecifically, possibly indicating 

 phenotypy (see P. epistomus, Plate 6, fig. P and Plate 8, fig. C). 



The length of article 6 in relation to the lengths of articles 4 or 5 

 is an important factor to be described, this article varying from shorter 

 than to much longer than article 5. 



Peraeopod 4. — In most of the species studied by the writer, the 

 fourth and fifth articles of peraeopod 4 are narrower than those of 

 peraeopod 3. In addition, article 2 is usually broader than in peraeopod 

 3 so that the disproportion between article 2 and the rest of the ap- 

 pendage is greater than in peraeopod 3. 



In most species there is little difference in width of articles 4 and 5 

 but in P. longirostris article 4 is quite inflated and much broader than 5. 



The length of article 6 in relation to either articles 4 or 5 must also 

 be taken into account. 



Peraeopod 5. — The structure of this appendage is quite useful in 

 differentiating between species. 



Some differences of note may be seen in articles 3 to 7, such as 

 slenderness, stoutness and proportionate length of the several articles. 

 Stoutness of articles 4 and 5 in P. obtusidens major (Plate 32, fig. Q) 



