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BULLETIN 2 1, UNITED STATES NATIONAL MUSEUM 



Remarks. — I give figures of four stages in the development of the 

 fourth pleopod of the male. Figure 32, a, is from a male specimen, 27 

 mm. length, figure 32, 5, from a male of the same length but showing 

 a slightly advanced condition of development, figure 32, c, from a 

 male measuring 30 mm. in length, and figure 32, d, from a fully adult 

 male, 37 mm. The general form of the pleopod is 

 laid down quite early, and in the pleopod of the 

 smallest male, 27 mm., the increase in length of the 

 distal joints of the endopod is already indicated. 

 This confirms Ortmann's observation on this point. 

 Progress to full maturity is marked by the greater 

 relative increase in length of the distal joint of the 

 endopod and its terminal spine, and in the gradual 

 increase in length of the setae of the whole pleopod 

 and their change from simple setae to plumose setae. 

 In the smallest pleopod figured none of the setae 

 are plumose, and they are all quite short and spine- 

 like. In the largest pleopod the setae are much 

 longer, and all but two or three on the distal joints 

 of the endopod have become plumose. This series 

 of pleopods is interesting as suggesting a means 

 whereby it is possible to judge the state of maturity 

 of male specimens of Mysidae, namely, the degree 

 to which the setae have become plumose. 



I also give a figure (fig. 33) of the fourth pleopod 

 of a male, 20 mm. in length, from Albatross station 

 4756, off the coast of British Columbia in 115 

 fathoms. It will be seen that it agrees in every 

 way with the pleopod from a male of 37 mm. taken 

 off Alaska. Nine females from this station aver- 

 aged only 22 mm. in length but all carried eggs or 

 embryos in the brood pouch. I have already noted 

 (1933) that specimens from British Columbia, col- 

 lected in depths from 50 to 120 fathoms, were much 

 smaller than Ortmann's types and were mature at 

 24 mm. I could not find any character, except size, 

 to distinguish these smaller specimens from the 

 large specimens from Alaska. Esterly (1914), in 

 noting this species from California, says that the 

 largest specimens measured 20 to 21 mm., but he 

 does not give any details as to the depth at which they were captured, 

 nor was he quite sure whether they were adult. It may be that there 

 is a more coastal race of this species, smaller than the deep-water race, 

 extending down the whole western coast of America from British 

 Columbia to California in depths of about 100 fathoms or so. The 



Figure 33. — Holme s- 

 iella anomala Ort- 

 mann: Fourth pleo- 

 pod of adult male, 

 20 mm., from Al- 

 batross station 4756, 

 X 20. 



