I2 CRUSTACEA MALACOSTRACA. III. 



Group I. Ianirini. 



Body oblong, considerably depressed. Head free. Eyes frequently present, situated on the upper 

 surface. Antennae with squama normally developed. Mandibles normal; molar process well developed, 

 directed a little forwards, with the end cut off. Palp of the maxillipeds with second joint considerably 

 or much expanded, and its two distal joints well developed. Thoracic segments freely movable. First 

 pair of legs frequently a more or less prehensile organ; the other pairs of walking legs of moderate 

 length, not increasing in length from second or third to seventh pair; accessory claw always discernible, 

 frequently robust. Uropods always on the lateral or the terminal margin, frequently well developed, 

 biramous, sometimes uniramous and, besides, much reduced. 



Remarks. The group comprises Icera Leach, Ianira Leach, Acanthaspidea Stebb., lauinila 

 Bonn., Katianira u. gen. and, besides, several genera not represented in our fauna, such as Ianiropsis 

 G. O. S., I&ropsis Koehler, Carpias Richardson, etc. The genera differ somewhat from each other in the 

 shape of the molar process, and considerably in the development of the first pair of legs, the length 

 and thickness of seventh joint with claw and accessory claw in all legs, the shape of the female 

 operculum and the development of the uropods. 



Ianira may be considered the typical and central genus of the group in all characters, while 

 Ianirella to some degree, and especially in the abdomen, constitutes a transition to Pleurogonium of the 

 group Munnini, and Katianira has a quite peculiar development of the first pair of legs. But in spite 

 of differences the genera are on the whole allied, showing gradual differences in the features enumerated 

 from genus to genus. 



laera Leach. 

 Only a single species is known from our area. 



i. Iaera albifrons Leach. 



1780. Oniscus marinus O. Fabricius, Fauna Groenl. p. 252 (not O. marinus L.) 



1814. Jcrra albifrons Leach, Edinb. Encycl. VII, p. 434. 



1838. Jam nivalis Kroyer, Kgl. D. Vid. Selsk. naturv. math. Afhandl. VII, p. 303; PL IV, fig. 21. 



! 1897. Jcrra marina G. O. Sars, Account, II. p. 104; PI. 43. 



1905. — — Richardson, Monograph, p. 450, figs. 503 — 504. 



! 1910. Icvra marina H. J. Hansen, Vid. Medd. Naturh. For. Kjobenhavn for 1909, p. 208, figs. 1—8. 



G. O. Sars and later authors have discarded the well-known name albifrons and applied marina 

 O. Fabr. Fabricius undoubtedly described the present species, but referred it to Oniscus marinus L. 

 It is impossible to interpret Linne's description, but Miers (1883) referred a collective species of Idothea 

 to O. marinus L., saying that a specimen of Idothea preserved in Linne's collection in the Linnean Soc. 

 London bears the name "marinus" "in what is undoubtedly Linnseus's handwriting". For these reasons, 

 and as the name I. albifrons is universally known, I prefer now to apply this name. 



In 1910 I pointed out that this species varies considerably in outline at Denmark. The spe- 



