neio Species of the Genus Solenopus 
323 
furrow (fissure) which occurs on the ventral surface, and 
within which the foot is concealed; there is, so to speak, a 
cleft for the foot; whereas “crescent” ( Neomenia ) really 
only applies to the species which Hr. Tullberg has described 
after the animal is preserved in spirits; for in the living state 
it has properly no crescent-shape; and as regards the other 
six species now described by us, it does not at all apply to 
them. 
We have already stated that Koren and M. Sars regarded 
Solenopus nitidulus as a mollusk; and our subsequent investi¬ 
gations have most decidedly confirmed this. But, as it differs 
considerably from previously known mollusks, we have not 
been able to bring it under any of the established orders of 
Mollusca, although it may well be referred to the great sub¬ 
class Opisthobranchiata of Milne-Edwards. We have accor¬ 
dingly formed for it a third order of Opisthobranchiata, which 
we have called Telobranchiata *, because the branchiae are 
situated at the hinder extremity of the animal. 
After what we have said above, of course we have been 
unable to adopt Dr. Ihering’s classification f with regard to 
the mollusk here treated of; for, although there is an anomaly 
in the generative organs of Solenopus nitidulus , which might 
indicate that, from a phylogenetic point of view, it was de¬ 
rived (had descended) from the Platyelmia, it is nevertheless 
certain that it is a true mollusk, and may be classified as 
such. 
We shall follow the brothers H. and A. Adams’s classifica¬ 
tion of the Gasteropoda. 
Subclass Opisthobranchiata, Milne-Edwards (1848). 
Order 3. Telobranchiata , Koren and Danielssen. 
The Telobranchiata are naked marine animals, with more 
or less worm-like bodies. They are hermaphrodite, and have 
neither tentacles, eyes, radula, or jaws. The foot is long and 
narrow, and can be completely concealed by the mantle. The 
branchiae, which are placed at the posterior extremity of the 
animal, are retractile. Heart with a pretty well developed 
vascular system. Body-cavity almost entirely filled by the 
visceral mass. Generative organs situated along the back, 
above the stomach and intestine. Nervous system composed 
* From re\os, end, and /3pay^ta, gills. 
t .Talirbiicher der Deutschen malakozoologisclien Gesellscbaft, 1876, 
Heft ii. p. 136 ; Vergleicbende Anatomie des Nervensystemes und Pbylo- 
genie der Mollusken, von II. von Ikering, 1877, pp. 81-42. 
23* 
