272 DISCOVERY REPORTS 



Atlanta peroni Lesueur, a species common in subtropical Atlantic waters, occurred in small numbers 



at the offshore station on the Orange river line on survey I. 



The pteropod Limacina was, however, numerically the most abundant mollusc in the collections. 

 Two species occurred, the first L. inflata (d'Orbigny) only in small numbers at the offshore station 

 WS 986. The other species L. bulimoides (d'Orbigny) also occurred at the same position, but was 

 principally found at the offshore stations on the Orange river line. Here it reached great concentrations 

 at the two stations WS 996 and 997. More than 3000 individuals were taken in the 250-100 m. haul 

 at station WS 997. 



We have seen (p. 229) that there was evidence of heavy grazing of the phytoplankton at these two 

 stations and this may well be attributed to these enormous numbers of pteropods. Also present at 

 these two stations were some specimens of the gymnosomatous pteropod, Pnenmodermopsis pancidens 

 Boas and its close association with the Limacina bulimoides and its probable feeding habits suggest that 

 it may have been preying upon the L. bulimoides. 



Two species of lamellibranch larvae occurred in the collections. Five hundred and forty individuals 

 of larva 'A' were taken in the 50-0 m. haul at station WS 981 off Walvis Bay. The other species, 

 larva ' B ' was present off Sylvia Hill at stations WS 988 and 989 and more numerously off the Orange 

 river mouth where 600 were taken at station WS 1002. 



Larvacea 

 The appendicularia from the samples, which include the genera Oikopleura and Fritillaria, have not 

 yet been identified, but some remarks may be made on the distribution of the group as a whole. 



Very large numbers occurred at the three inshore stations on the Walvis Bay line (WS 979, 980 and 

 981) reaching a maximum of about 5400 in the 50-0 m. haul at WS 980. The numbers fell off sharply, 

 however, and only five individuals were present between 500 m. and 100 m. at station WS 978. 

 At the stations seaward of this, modest numbers occurred in the surface-layers. 



On the Sylvia Hill line of stations, a reversal of these conditions was observed. At the outermost 

 station, WS 986, fairly large numbers occurred in all of the hauls. At WS 987 none of the hauls 

 contained appendicularia. At station WS 988, large numbers (> 200) were again encountered in 

 both the 50-0 m. and 100-50 m. hauls and at the station nearest the coast numbers decreased once 

 more. 



This distribution was nearly paralleled on the Orange river line, where virtually all of the appendi- 

 cularia occurred at the two offshore stations. None was present inshore at stations WS 1000, 1001 and 

 1002. At the offshore stations numbers were highest in the surface -layers, and decreased with depth. 



The explanation of this distribution is not easy without a more specific identification of the indivi- 

 duals. It may conceivably be the result of the presence of two separate populations of appendicularia 

 — the first, in abundance inshore at Walvis Bay and extending southwards to WS 988 and 989 at the 

 inshore end of the Sylvia Hill line, and the second, offshore on the Orange river line and Sylvia Hill 

 line (WS 986) and extending northwards in decreasing numbers to the offshore end of the Walvis Bay 

 line. Confirmation of this suggestion, will, however, have to await a more detailed examination of the 

 species. 



Eggs and young stages of fish 

 Hart and Marshall (1951) have already commented on the fish-eggs and larvae which occurred in the 

 plankton hauls. Of particular interest were the large numbers of eggs and larvae of Sardinops sagax 

 ocellata, which occurred at the inshore end of all of the lines of stations, but particularly at the inshore 

 stations on the Walvis Bay and Sylvia Hill lines. The greatest catch of 1000 eggs was taken in the 



