184 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 18 



blank spaces of this chart that many of the species were poorly known. 

 It is hoped that zoologists having access to the species concerned will 

 examine them and determine the unknown criteria. Only then, can an 

 attempt be made to construct a zoogeographic flow-chart of criteria. 



The differentiating characters used in this study represent those 

 deemed to vary the least intraspecifically but to vary the most inter- 

 specifically. The following characters are important not only from 

 this viewpoint but because they are easiest to observe in undissected 

 specimens. 



In the diagnoses of the species in the systematic section uniform 

 generic criteria are not mentioned. 



A section on minor criteria will follow this discussion. 



Head. — Little attention has been paid to the dorsal view of the 

 rostrum in the past and it is entirely unknown in many species. Since 

 a narrowed rostrum can scarcely be overlooked, it has been assumed 

 in Table 1 that the rostrum is broad for those species in which it has 

 not been described. 



Two major rostral types occur, the broadened one with straight or 

 slightly convex lateral edges, tapering evenly to the apex (Paraphoxus 

 ss.) ; and the abruptly narrowed one which is called the modified or 

 trichophoxid rostrum (Trichophoxus ss.). In the modified type the 

 styliform section may be broad (P. epistomus) or quite narrow (P. ab- 

 ronius). Species with a normal rostrum may be distinguished from each 

 other by the difference in total head length. For example, P. obtusidens 

 and P. spinosus are scarcely distinguishable except for the longer head, 

 smaller eyes and larger body size of the former species. 



Body. — The body proportions of paraphoxids vary so much that it 

 is possible to isolate species superficially on the basis of their general 

 appearance. This is best illustrated when the two species P. obtusidens 

 (Plate 33, fig. A) and P. tricuspidatus pallidus (Plate 38, fig. B) are 

 compared. Gross inspection would certainly indicate that they belong 

 to separate genera but detailed analysis reveals no basic generic dif- 

 ferences. Paraphoxus bicuspidatus has a very broad, dorsally flattened 

 and laterally expanded body, with the urosome disproportionately small, 

 whereas P. obtusidens has a rather slender, uniformly tapered body. 



Epistome. — Until Shoemaker 1938 discovered the presence of an 

 acutely produced epistome in P. epistomus, it was generally known 

 that the Phoxocephalidae lacked a cuspidate epistome. Other species 



