17 
several polyps having less than 4, or even none at all. Moreover 
the gonophores of K. danæ have only 3 tentacles, not 4 as in P. 
sulfureus (the figure represents a gonophore with 4 equally devel- 
oped, expanded tentacles). According to Steche the polyps are 
surrounded by a perisarc (“Periderm”), distinguished from that of 
other Perigonimus-species by the lack of foreign bodies. If there 
really is a perisarc, P. sulfureus is a true Perigonimus and consti- 
tutes a connecting link between the ordinary members of that 
genus and Kinetocodium, to which it is evidently related. 
Remarks on other species of Hydroids occurring on 
Pteropod shells. 
It is curious that nobody has ever taken up the idea to deal 
with the hydroids growing on pteropod shells. The matter seems 
rather inviting for study, but our knowledge is restricted to a few 
scattered remarks in the literature. Boas (1886, p. 34) found 
hydroid colonies on the following species of pteropods: Cleodora 
balantium , Cl. cuspidata, Cuvierina columella, and Hyalæa trispi- 
nosa. As far as the latter species is concerned, hydroids were 
particularly found on specimens from the South Atlantic and the 
Indian Ocean. The hydroids were not identified. Setting aside the 
problematic occurrence of Perigonimus repens on Hyalæa tridentata 
(mentioned above), altogether five species of hydroids are found 
on pteropod shells, viz. Kinetocodium danæ (the new species de- 
scribed in the present paper), Perigonimus sulfureus Chun (men- 
tioned above), Campaniclava cleodoræ (Gegenbaur), Campaniclava 
clionis Vanhoffen , and Laomedea striata (Clarke). None of these 
five species are known to occur on any other kind of support. — 
I shall give a short account of the material which I have found in 
the collection of pteropods in the Zoological Museum of Copen- 
hagen. — The State of preservation is very bad; accordingly I 
can give practically no additions to the morphology of the species; 
but the statements of the geographical distribution are rather sur- 
prising, considering the previous knowledge of the matter. 
Vidensk. Medd. fra Dansk naturh. Foren. Bd. 74. 
2 
