72 Studies on Arthropoda. I. 



around this 8 or 9 extremely minute, oblong pits. In /. emar- 

 ginata F. and /. ungulata Pallas organs somewhat similar to 

 those in I. balthica are found. 



Among other animals belonging to the sub-order Valvifera 

 Mesidothea sibirica Bir., M. Sabini Kr., and Arcturus Baffmi 

 Sab. have been inspected, but with negative result. 



Serolis. 5. paradoxa Fabr. has a very distinct though 

 somewhat small, a little oblong, depressed area near the posterior 

 margin of the head; the area has several tiny pits, especially 

 near the masgin. S. Schythei I/tk. has a similar nearly circular 

 area. 



Bathynomus. In B. giganteus A. M.-Edw. an organ was 

 discovered, briefly described and figured by me in 1903 (see 

 p. 68). I have examined a large immature female. Near the 

 posterior margin of the head it has a most conspicuous, whitish 

 spot, which does not show the numerous, irregularly impressed 

 points on the surrounding brownish chitine. The spot is as a 

 whole a little arched but depressed along the middle; each half 

 has a small group of 6 or 7 minute pits ; the median part has a 

 very oblong area well marked off by an depressed line and with 

 a linear depression in the median line; somewhat behind each 

 group of pits is found a shallow excavation which has a number 

 of oblique, parallel, impressed strise ; at the front end of the area 

 is seen a group of some nearly rudimentary pits. 



Cirolana. In C. borealis L,illjeb. a very small group of three 

 to six tiny pits is found near the posterior margin of the head; 

 they are sometimes situated in a very shallow or very distinct 

 depression. A specimen of C. Rossii Miers has some irregularly 

 scattered minute pits. 



Mga psora L. and specimens of Rocinela, Anilocra and Cy- 

 mothoa have been inspected with negative result. 



Among the sub-order Asellota Asellus aquaticus L., Mun- 

 nopsis typica M. Sars and Munnopsurus giganteus G. O. Sars, 



