72 U.S. NATIONAL MUSEUM BULLETIN 23 6 



somite. Distal ventral border of 2nd abdominal somite witb, on 

 right and left side, indistinctly formed lobe, bordered by very fine 

 spines (fig. 216). 



Rostrum semicircular, curved plate, covering basal parts of anten- 

 nules. Antennules 5-segmented; segment 4 elongate, slightly swollen, 

 forming joint with 5th segment, which apparently results from fusion 

 of several smaller segments. Antenna and mouth parts not studied 

 in detail. 



The legs have the following setal formula : 



There are practically no differences in the structure of legs 1 to 4 in 

 the sexes; the only difference I could detect is the slightly more 

 proximal insertion of the spines along the external border of the exop- 

 odal segments (figs. 22a-d). 



Leg 5 with exopodite and baso-endopodite well separated and of 

 nearly the same length. Baso-endopodite with 2 spiniform setae of 

 imequal lengths, external being much smaller. Exopodite with 4 

 setae; lengths and positions can best be taken from figure 22e. Exter- 

 nal seta of baso-endopodite fine, placed on sHghtly elevated part. 



Color transparently yellowish-green; contents of gut and fecal 

 pellets visible as darker, green-brown spots in body. No eye or eye- 

 spots visible. 



Remarks. — As also appears from the setal formula, there are 3 

 spines at the external margin of the 3rd exopodal segment of the 1st 

 and 2nd leg and 2 on the same segment of legs 3 and 4. In Ectinosoma 

 (Ectinosoma) tenuipes T. and A. Scott, 1894, a closely allied form, there 

 are 3, 3, 3, and 2 on the corresponding segments of legs 1, 2, 3, and 4, 

 respectively. The total number of appendages on the 3rd exopodal 

 segment of these legs is 6, 7, 7, 7 in E. dentatum and 6, 7, 7, 6 in E. 

 tenuipes, but on the 3rd leg the same number of appendages have a 

 different distribution. This characteristic, which is also mentioned 

 by Steuer (1940, p. 126) in his original diagnosis oi E. dentatum, appears 

 to have escaped Lang's attention but may serve to separate both 

 closely related forms. The threadlike spinules on the cephaHc somite 

 are easily removed and the above-mentioned additional, differentiat- 

 ing characteristic may be of particular importance in the males, where 

 the differences in the structure of leg 5 between both species are 

 minute, 



E. dentatum was described originally from Anfouchi Bay near the 

 port of Alexandria, Egypt, in the eastern Mediterranean, from a 



