E. SIM I LIS VAR. ARM AT A 



237 



the parent species by having the third abdominal segment " carinated posteriorly in the 

 median line and produced into a compressed, somewhat short, but very conspicuous, 

 acute process". I have found that the process may be very variable in size and shape; 

 it varies from being low, rounded and inconspicuous to being a large compressed spine 

 pointing backwards over the fourth segment (Fig. 24 c). There is no doubt that Tatter- 

 sall was right in regarding Zimmer's variety lobata as the same as Hansen's armata. 



Specimens with the process spine-shaped are more common than those with a 

 rounded process in the waters from which my material comes. I have re-examined, 

 since identifying them at sea, 459 specimens of the variety armata drawn from thirteen 

 different stations. 400 of them, drawn from all the stations, had the process on the third 

 abdominal segment spined, forty-nine from six of the stations had the process rounded. 

 Of the thirteen stations two were near the Cape, one south of the mid-Pacific, the others 

 south of Australia. Those with the process rounded came from the stations south of 

 Australia, but I have no doubt that the rounded process occurs throughout the range 

 of the species in similar latitudes ; I have seen it in specimens from the south-west 

 Atlantic and from south-west of the Cape. Specimens with the rounded process 

 occurred in the warmer of the thirteen stations and were most numerous in the warmest 

 of them. 



The greatest number of E. similis var. armata to be taken in one net was 265 in the 

 oblique haul with a metre net from 1 17 m. to the surface at the station east of Tasmania. 

 They were immature and there were no E. similis in the same net. (In the deeper net at 

 the same station, a metre net fished obliquely from 315 to 120 m., there were four 

 E. similis and twelve var. armata). One hundred of the specimens from the shallow net 

 were examined to see how many had the process spined and how many rounded: the 

 numbers were seventy-six and twenty-four, and their lengths were as follows: 



I do not, however, think that whether the process is rounded or spined is a question 

 of age; I have seen specimens only 10 tnm. long with the process strongly spined. 



The antennules of the var. armata with strongly spined processes have the charac- 

 teristic structures more strongly developed than in E. similis: the keel on the second 

 segment is higher and transparent, and the process at its end stronger and sharper ; the 

 process at the outer distal corner of the second segment is stronger ; the dorsal keel on 

 the third segment is higher and more arched. 



