Studies on Arthropoda. I. 



surface of the head it is generally possible to perceive a faint 

 vestige of a median protuberance situated not inconsiderably 

 behind the base of the movable rostral plate. 



2. Anaspidacea. 



Anaspides tasmania G. Thorns. Caiman described and 

 figured a very conspicuous dorsal organ (Trans. Roy. Soc. 

 Edinburgh, XXXVIII, 1896). Nothing is to be added. 



Paranaspides lacustris Geoff. Smith. The organ is more 

 reduced than in Anaspides, as there is no pigmentation; the very- 

 small pits are irregularly arranged, and their number in three 

 specimens varies from 3 to 5. 



3. Mysidacea. 



Gnathophausia. In a gigantic specimen of G. mgens Dohrn 

 a part of the dorsal keel a little in front of its base and about 

 15 mm. long is flattened above and behind the middle distinctly 

 thickened, this narrow area has a pair of very conspicuous, 

 very oblique, convex spots marked off all around by an de- 

 pression, and the spots look almost as scars. In G. zoea Will.- 

 Suhm about one mm. of the dorsal keel above the mandibles 

 is, seen from above, rather considerably thickened but not flat ; 

 seen from the side with the light transmitted the dorsal chitine 

 of this part is thin and the contents opaque, indicating that the 

 tissue is of another quality than in the surroundings. 



Eucopia. --In one specimen of E. sculpticauda Faxon a 

 nearly circular, somewhat shallow depression situated above 

 the mandibles somewhat in front of the anterior transverse 

 furrow; the depression has a minute, dark point as if a scar 

 after a prick with a needle. In another specimen the depression 

 is wanting, but the dark point exists; in a third specimen noth- 

 ing could be seen with certainty. In specimens of E. ungui- 

 culata Will.-Suhm nothing was found. 



