346 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



Parathemisto abyssorum (Boeck), Thorsteinson, 1941, pp. 90-91. 

 Parathemisto japonica Bovallius, Hurley, 1956, pp. 15-16. — Vinogradov, 1956, 

 pp. 211-212. 



Diagnosis: Total length of adult 9, excluding antennae, 4.5-8.5 

 mm. Body more chunky in appearance than in most species of 

 Parathemisto. Dorsal to antennal groove head is less roundly pro- 

 duced in lateral view than in P. abyssorum, i.e., slope of this part of 

 head is directed more posteriad than in P. abyssorum. Pleonites with 

 a few minute teeth along ventral margins, posterior lateral corners 

 produced into small points. Female antenna 2 about as long as 

 antenna 1, slightly shorter than head plus first 2 pereonites. Molar 

 process of mandible about twice as long as incisor process. Max- 

 illiped with row of long spines at distal end of basal pJate. Propodus 

 of Pi serrate but not spinous on posterior margin. In length 

 P6>P7>P5. Posterior distal corners of carpus of P6-7, but not 

 of P5, with conspicuous spines. Dactyls of P5-6 pectinate at base. 

 Peduncle of uropod 3 from 2 to 2.5 times as long as telson. 



Kemarks: K. H. Barnard (1930, p. 419) suggested that Stebbing's 

 P. pacifica was a synonym of P. japonica. Barnard did not have 

 specimens of either species, and his conclusion was a reasonable one 

 to draw from a comparison of the descriptions by Bovallius and 

 Stebbing. I suspect that Stebbing would have reached the same 

 conclusion, for at the time he described P. pacifica, Bovallius had 

 published only a brief, unillustrated description of P. japonica. If 

 Bovallius' more detailed and illustrated description published in 1889 

 had been available to Stebbing, he might not have described P. pa- 

 cifica as a separate species, for the differences emphasized by Stebbing 

 and listed below are actually not valid for distinguishing the two 

 species : 



1. The propodus of P3 of P. pacifica is longer than the carpus and 

 is pectinate rather than smooth on the posterior margin. While 

 Bovallius (1889) states that the propodus is a little shorter than the 

 carpus, he also says that the propodus is finely pectinated, and in 

 his figure 35, plate 12, it is shown as pectinate and slightly longer 

 than the carpus. 



2. In P. pacifica, the outer ramus of uropod 3 is shorter than the 

 inner ramus. Although Bovallius (1889) states that the two rami 

 are of equal length in P. japonica, his figure 43, plate 12, shows the 

 outer one to be slightly shorter. Stebbing does not say how much 

 shorter the outer ramus of P. pacifica is, and provides no figures. In 

 my specimens of P. japonica and P. pacifica, the outer ramus is slightly 

 shorter. 



Although the above criteria are worthless for distinguishing between 

 P. pacifica and P. japonica, I nevertheless consider them as distinct 



