180 BULLETIN 201, UNITED STATElS NATTOHSTiAL MUSEUM 



also able to record the presence of two sternal processes in N. americana 

 but have failed to detect them in any species of the genus Acanthomy- 

 sis. These processes have now been found in nine species of the 

 genus Neomysis {sensu stricto) and in no species of the genus Acan- 

 thomysis. Only one species of Neomysis, N. spinosa, has so far been 

 found to be without them, but N. patagona, N. monticelli, and N. 

 meridionalis still await examination from this point of view. Ii 

 says that these processes are present in N. japonica, but in the material 

 of this species at my disposal I failed to detect them. 



There is a small rudimentary oostegite on the sixth thoracic limb 

 in several species of this genus, similar to those on the fifth and sixth 

 limbs in the genus Mysis. I have found such oostegites in N. rayii, N. 

 hadiakensis, N. mercedis, N. mirabilis, N. czemiawskii, N. americana, 

 and in one species of the genus Acantliomysis, A. dybowskii. It seems 

 likely that they are present in all species of these two genera. 



In 1932, I attempted a provisional grouping of the species of the 

 genus Neomysis (sensu lato) based on the antennal scale, spines on 

 the inner uropod and the form of the telson. As stated above those 

 species with a rounded apex to the antennal scale have since been sep- 

 arated off under the genus Acanthomysis. The remaining species, 14 

 in number, now form the genus Neomysis {sensu stricto). The fol- 

 lowing key will serve as some guide to their identification. It is a 

 modification of the key suggested in 1932, based on a more extended 

 knowledge of the species. 



KEY TO THE SPECIES OF NEOMYSIS 



a 1 . Free thoracic somites and all abdominal somites smooth, without furrows or 



ridges. 



b 1 . Inner uropod with a dense row of spines on lower surface near statocyst, 



at least 10 in number and often as many as 80 to 90. 



c 1 . Telson short, apex broadly truncate, spines on lateral margins few and 



widely spaced without small spines between them.awatschensis (p. 190) 



intermedia (p. 188) 



mercedis (p. 187) 



c 2 . Telson long and narrow, triangular in shape, apex narrowly truncate, 



spines on lateral margins numerous and rather widely spaced without 



small spines between them rayii (p. 181) 



integer (p. 247) 



c 3 . Telson long and narrow, triangular in shape, apex narrowly truncate, 



almost rounded, spines on lateral margins numerous, rather crowded, 



without small spines between them kadiakensis (p. 192) 



japonica (p. 194) 



c 4 . Telson long and narrow, triangular in shape, apex rounded, lateral spines 



numerous, crowded and on part of margin at least, arranged in groups 



of larger spines with smaller spines between them.. americana (p. 195) 



spinosa Nakazawa, 1910 



