4 EISEN, PRELIM. REPORT ON GEN. AND SPEC. OF TUBIFICIDA. 
organs, which according, to our present ideas are the only 
ones, which. can furnish characteristics to distinguish genera 
and species. 
That the presence of hair-spines, which is said to di- 
stinguish Tubifex from Limnodrilus hardly can be considered 
as a generic characteristic, is clearly seen by studying the 
genus Hemitubifex. The only species of this genus has ge- 
nerally both hair-spines and forked spines, but sometimes we 
find individuals with no hair-spines at all, all being short and 
forked. Other individuals have some few hair-spines inter- 
spersed among the forked ones. We would here have suf- 
ficient grounds to classify the same species in two very 
different genera, at least if attention was paid to only exter- 
nal characteristics. 
This genus is also remarkable in an other respect. The 
upper end of its atrium is enlarged to a globular ”vesicula 
seminalis”, similar to that which, according to VEJDOVSKY, 
should characterize the genus Psammoryctes. But as Hemi- 
tubifex has no comb-like spines, and as the lower end of its 
atrium is glandular, as in most of the genera, I think there 
is reason enough to consider it entirely distinct from other 
new and old genera. This shows however that only a com- 
bination of characteristics can suffice to characterize a genus, 
and that the mere presence of different kinds of spines not 
always is enough to distinguish a genus from another, and 
also that anatomical differences should be the deciding ones 
in regard to both genera and species. 
Of the other new genera, the genus Spirosperma is well 
characterized by its spermatophore, which is extended and 
spiral, and also by its conical cephalic ganglion. 
Ilyodrilus has an emarginated ganglion, and an extremely 
short efferent duct, and is well distinguished from its allied 
genera. All these genera have hair-spines, and some of them 
also comb-like spines. 
The genera with only forked spines are two, viz. the 
old genus Limnodrilus and the new genus Camptodrilus, 
which I have separated from the former on account of its 
having peculiar spiral muscles round its copulative organs. 
The new genus Telmatodrilus is perhaps the best cha- 
racterized in the family, and so unlike the other genera, 
that I prefer to place it in a separate sub-family. The mul- 
