Chaetognaths off Peru — Bieri 
261 
has a distribution similar to S. minima but 
occurs somewhat deeper than that species. In 
1952 it occurred at every station off Peru 
while in 1941 a single specimen was taken at 
station 7. Much of this difference is no doubt 
due to the fact that the 1952 net tows were 
oblique to about 300 meters, but more ex- 
tensive sampling of the surface waters off 
Peru may show that Sagitta sp. was unusually 
scarce there in 1941. A specimen belonging 
to the serratodentata group was taken at station 
13 and is for convenience called S. serratoden- 
tata atlantica since it most closely fits the 
description given by Thomson (1947). It is 
considered for the present to be a form of 
S. pacifica and part of that population. 
Sagitta tenuis (Fig. 13) occurred at 12 sta- 
Fig. 10. Distribution of Sagitta regularis in 1941 and 
1952. Crosses with hatchure — present 1952, without 
hatchure — absent 1952. 
Fig. 11. Distribution of Sagitta robusta in 1941 and 
1952. Crosses with hatchure— present 1952, without 
hatchure— absent 1952. 
tions in 1941. The taxonomic status of this 
species has been in doubt for many years. 
Most workers (Faure, 1952; Fraser, 1952; To- 
kioka, 1955) have kept S . tenuis and S. friderici 
as separate species. The author also held this 
opinion for some time; however, in the 1941 
Peru material a complete set of intergrades 
exists between S. friderici to the south and 
5. tenuis to the north. The same situation has 
been observed by the author in samples taken 
off Lower California except that there the 
tenuisAske form is to the south and th e f rider ici- 
like form to the north. Michael (1911) called 
this species Sagitta bipunctata. In view of these 
intergrades, it would appear that S. tenuis and 
S. friderici are ecotypic variants of a single 
interbreeding population or species. Because 
