174 
give due allowance for future finds, I should consider it unlikely 
that outposts may occur north of 50^ Northern Latitude. 
An outstanding feature in the geographical occurrence of the 
Stylochids is undoubtedly the faet that they have their main distribution 
in tropical and subtropical areas. In addition they inhabit temperated 
zones, but chiefly the Southern parts of these. In the family, Sty- 
lochus is the predominating genus, and at present it really flour- 
ishes with a great number of species, Their size and the strength 
of body present striking features. The largest Polyclad I have ever 
collected was a Stylochus (from Misaki in Japan) and it attained 
alive a length of more than 1 dem. In preserved State it surpasses 
7 x 7 cm. Meixner also points out how the Stylochids in the tro- 
pics reach considerable sizes (“60 mm und daruber“). A similar 
tendency to gigantic growth of specimens in warm seas is met 
with in Planoceridae, a family having a distribution very similar 
to Stylochidae, and as examples I shall take Paraplanocera disens 
from Mid-Pacific and Planocera reticulata from Misaki. Among the 
Cotylea the tropical Pericelis Beyerlana (Collinswood) oceurring from 
Somali at least to the Gilbert Islands and Fiji reaches an impres- 
sive dimension. The striking differences in size between the Poly- 
clads of the Boreal fauna compared with those of the Mediterra- 
nean is also noteworthy here. Pseudoceridae, a Cotylean family,. 
having a distribution similar to Stylochidae, luxuriates in the tro- 
pics in number of species as well as in size, but above all in the 
most splendid colours. 
We have thus a close resemblance between Stylochidae, Pla¬ 
noceridae, and Pseudoceridae with regard to the geographfcal distri¬ 
bution and they are all typical inhabitants of warm seas. This ge¬ 
neral feature in the occurrence of these families cannot be ex- 
pected to be altered in any pronounced way through an inerease 
of our knowledge of the Polyclad faunas. Even if some outposts 
might be known in the future they will only constitute exceptions 
to the rule. 
Here I may also mention that I must regard some very char- 
acteristic Polyclads of the Boreal fauna; i. e. Discocelides, Poly- 
posthia, and Cryptocelides as a kind of substitute for the missing 
Stylochids. I consider these forms, together with the genus Plehnia 
(PI. arctica and japonica) as not distant relatives of the Stylochidae.^ 
