PART 1 GARTH : PACIFIC OXYRHYNCHA 347 



Pleopod 1 like that in the [Pisinae Alcock]. Pleopod 2 short. (Steph- 

 ensen ) 



While the key that follows permits the further division of the Mith- 

 racinae thus broadly conceived into the Mithracinae, sens, restr., and 

 the Macrocoelominae of Balss (1929, p. 16 ff.), this refinement is not 

 adopted here for reasons set forth in the introduction and again dis- 

 cussed for the subfamily Pisinae. The presence of the intercalated spine, 

 on which Balss based the separation of the Mithracinae from the Macro- 

 coelominae, is difficult to demonstrate in Hemus< Thoc, and Teleophrys 

 because of coalescence. The genus Microphrys, placed by Balss in the 

 Macrocoelominae, has an intercalated spine and must on this account be 

 considered as belonging to the restricted mithracine group. Furthermore, 

 it shares with Ala [=Anaptychus], said by Balss to have been derived 

 from the Hyasteniinae, a typically mithracine male first pleopod. Finally, 

 Stenocionops and Macrocoelorna themselves stand close in structure of 

 pleopod to Libinia and Neodoclea of the Hyasteniinae (here considered 

 a subgroup of the Pisinae) and may be related to them through Coelo- 

 cerus, an Atlantic genus not seen by Balss, nor yet studied by the present 

 writer. 



Key to the American Genera of the Subfamily Mithracinae 



(Pacific genera are shown in bold-face type and are treated in this work) 

 (Basal antennal article forming floor of orbit; intercalated spine present 



or absent) 

 la. Intercalated spine present; orbits sometimes projecting beyond 



general outline of carapace, but never tubular .... 



(Mithracinae, sensu restr., Balss) 



2a. Orbits not projecting laterally beyond general outline of 

 carapace. Carapace subtriangular. Legs cristate 

 3a. Merus of ambulatory legs with a thin, lamellate, pos- 

 terior expansion. No preorbital tooth 



4a. Carapace very high on median line. Basal article 

 of antenna broader than long . . . Hemus 



4b. Carapace not noticeably high on median line, 

 lobulate. Basal article of antenna no broader than 



long Thoe 



3b. Merus without posterior (or inferior) expansion, but 

 cristate above. A preorbital tooth present 

 Teleophrys 



