SPECIES PRESENT IN THE SAMPLES 263 



these depths were 4-60° C. and 1-85° C. respectively). The description was brief and even failed to 

 give adequate details of the unsymmetric glands. The same author (1894) ascribed material from the 

 Mediterranean to the same species. The length of typical specimens in this material was only o-8 mm. 

 as opposed to 1-15 mm. in the case of the Pacific material, and there were fewer pairs of spines on the 

 principal seta of the male antennule (eight instead of ten). The frontal organ of the male also differed. 



The ' Valdivia ' Expedition provided a large quantity of material from the Atlantic and Antarctic 

 including species allied to C. rotundata, which Miiller (1906) distinguished and named. It included 

 material which resembled his previous specimens of C. rotundata, and also longer specimens (up to 

 1-75 mm. in length) with similar features, such as the position of the unsymmetric glands. He in- 

 cluded the longer forms in the same species. He noted that the 'long forms' were typical of the 

 Antarctic and the ' short forms ' of warmer waters, but assumed that he was dealing with a very 

 variable species. 



Fowler (1909), while studying the planktonic Ostracoda of the Bay of Biscay, obtained specimens 

 of both the ' long ' and ' short forms '. He interpreted the two ' forms ' on the basis that the ' long forms ' 

 were adult and the 'short forms' juveniles of the same species. 



Further material from the Antarctic was examined by Skogsberg(i92o). He obtained specimens of 

 the ' long forms ' and described them in some detail, noting that they agreed with the ' long forms ' 

 described by Miiller. He did not find any of the ' short forms ', considered that Fowler was mistaken 

 in supposing them to be juveniles, and decided that they belonged to a nearly related species, possibly 

 C. nasotuberculata. He concluded in fact that Muller's C. rotundata might be a mixture of closely 

 allied species. 



The samples collected by the ' William Scoresby ' in the Benguela current provide further material 

 of both the 'long forms' and the 'short forms' of C. rotundata as described by Miiller (1906). Both 

 these ' forms ' occur at the same stations and in some instances in the same samples. There are fully 

 matured male and female specimens and also juveniles of each type. The use of closing-nets and the 

 numbers of adults of each form in each sample shows that there is a clear difference in their depth 

 distribution. Table 1 gives the total number of 'short forms' of C. rotundata taken at the different 

 stations, and the proportion collected at depths above 250 m. is compared with the figures for the 

 ' long forms ' and for C. nasotuberculata. Only one specimen from a total of twenty-three ' long forms ' 

 was captured above 250 m., whereas many more 'short forms' occurred in samples taken above 

 250 m. than below. C. nasotuberculata, clearly distinguishable morphologically from the ' short forms ', 

 occurs in the same samples. Its depth distribution (Table 1) falls somewhat between that of the two 

 ' forms ' under consideration. 



Table 1. Comparative depth distribution of 'long' and 'short forms' of 

 C. rotundata and C. nasotuberculata 



