1914] Esterly: Schizopoda of the San Diego Region 7 



the third joint is provided on the dorsal surface with a delicate 

 lamella which runs lengthwise of the joint (pi. 2, fig. 19). The first 

 joint is about as long as the second and the third together, and the 

 third is three-fourths the length of the second. 



The males are identified by the structure of the inner part of the 

 first pleopod. The appearance of this as generally seen under the 

 microscope is shown in plate 2, figure 23, while figure 18 shows the 

 appearance of the organ as seen somewhat from the side. The hood- 

 like structure in figure 23 is the median lobe and it carries the hooked 

 lateral process and the short spine-like additional process ; the 

 terminal process is shown at the left of the figure and the proximal 

 process lies between it and the median lobe. Hansen's description 

 of the organ is as follows : ' ' Terminal process of the copulatory 

 organs moderately short, a little thicker than in two other species, 

 a little expanded toward the end, with the outer ramus only a short 

 tooth and the inner very much longer but bent much forwards. The 

 proximal process somewhat longer than the terminal, without any 

 secondary branch beyond the middle, while the distal part is some- 

 what expanded, forming a plate which is much longer than broad, 

 with the terminal margin rounded and only feebly emarginate some- 

 what from the broadly rounded end. Lateral process without tooth 

 on the distal part." Hansen's figure does not show the small spine 

 on the median lobe which evidently corresponds to the additional 

 process ; .he states (1910, p. 79) that in all species of Euphausia known 

 to him the median lobe lacks an additional process. E. pacifica was 

 described in 1911 and the fact that the additional process is present 

 should be added to his account. This author neither mentions nor 

 figures the lamella with the finely serrate distal margin shown on 

 the proximal process in figure 23 (plate 2) ; in some cases a consid- 

 erable part of the edge of the plate of the process is finely serrated. 

 Such differences as have been mentioned between our specimens and 

 those described by Hansen are doubtless unessential and I do not 

 hesitate to identify the San Diego forms as E. pacifica Hansen. 



The larger individuals of both sexes are from 20 to 25 mm. long. 



Hansen states (1911, p. 29) that pacifi,ca is very common in Jap- 

 anese waters ; it is abundant here. 



Hansen's third group of the species of Euphausia consists of those 

 having one pair of lateral denticles on the carapace and a dorsal keel 

 on the third segment of the abdomen. This is the so-called " gibha 

 group ' ' and our only species is the following. 



