PART 1 GARTH : PACIFIC OXYRHYNCH A 13 



the accompanying male pleopods of C. angulatus Rathbun and C. tanneri 

 Rathbun are those of immature, the pleopod of C. opilio (O. Fabricius) 

 of mature, specimens. 



The Male First Pleopod 



While the study of the male first pleopods was undertaken with the 

 thought that differences encountered would be of value in separating 

 species of doubtful distinctness, an unexpected result has been the dis- 

 covery of general similarities at generic and subfamilial levels. The 

 Inachinae, with the removal of Oregonia, are remarkably uniform with 

 respect to pleopod. The Acanthonychinae are clearly of two types: those 

 with a scyriform pleopod, related to Chorilia of the Pisinae, on the one 

 hand, and those with an epialtiform pleopod on the other. The Pisinae, 

 with the removal of Hyas and Chio?ioecetes, are also of two main types, 

 the scyriform and the pisiform, while a third type relates Neodoclea and 

 Libinia to Stenocionops and Macrocoeloma of the Majinae, sensu lato. 



The writer would make further present use of these pleopod group- 

 ings, which in the Acanthonychinae, Pisinae, and Majinae cut across 

 recognized subfamilial lines, except for two important considerations: 

 ( 1 ) in each subfamily as now constituted there are two or more genera 

 with anomalous pleopods which are not assignable with any certainty to 

 any of the above groupings; and (2) the premature application of any 

 new system to the New World segment of the Majidae without the 

 inclusion of the Old World segment as well might add to the confusion 

 which it is hoped to correct. 



It is equally apparent from a study of the pleopods that some genera, 

 as well as subfamilies, are diphyletic. This is most apparent in Rochinia, 

 where R. vesicularis alone has a scyriform pleopod, whereas the remain- 

 ing species examined have the pisiform pleopod. Other genera, like 

 Hemus, show no uniformity, each of the three species of Hemus exam- 

 ined having a pleopod of a strikingly different type. Still other genera, 

 such as Mithrax, which conform in the main, have aberrant species, 

 notably M. belli and M. nodosus, which have completely anomalous 

 pleopods. Use of this character, therefore, has been approached with 

 extreme caution, and has been employed to effect major systematic 

 change only when substantiated by some more firmly established char- 

 acter. 



Regarding the terminology employed in discussing the male first 

 pleopod, the writer can do no better than to quote Tweedie (1940, 

 p. 88) : "The terminology used in describing the structure and orientation 



