65 
found on the buccal plates, a character found alone in Ech. escu- 
lentus among the Echinoids of the Scandinavian Seas. Also the 
structure of the spines is as in esculentus (comp. ,,Ingolf"-Echinoidea I. 
Pl. XX, Fig. 30). The pedicellariæ åre as usual in escu/entus. 
The colour of the test is pink, not the deep red characteristic of 
esculentus. — The genital pores are well developed, the specimen 
having thus evidently had the genital organs well developed. 
If this specimen had come from a locality, where the existence 
of some unknown EÆEchinus-species could not beforehand be denied, 
nobody, I suppose, would have hesitated to declare this specimen 
to represent aå new species. The whole appearance is very unlike 
that of esculentus, and especially the character of the ambulaera, 
being of primary importance among the Echinus-species (and upon 
the whole among the Echinina), would make it almost inevitable 
to regard it as a new specific type. But the Danish Seas are so 
well known that the suggestion of a hitherto unknown, large species 
of Echinus, with well marked characters, existing there must seem 
quite absurd. The result is then that the specimen must be a 
hybrid, the question being only, which species should be regarded 
as the parents. 
Only three species of regular Echinoids occur in the Sound, 
viz. Parechinus miliaris, Echinus esculentus and Strongylocentrotus 
drøbachiensis. It is, however, only the last named, which occurs 
commonly here, and especially Ech. esculentus is very rare. Never- 
theless there cannot be the slightest doubt that Ech. esculentus 
is one of the parents, the specimen agreeing in most of it 
characters with this species. The other parent species very pro- 
bably is Parechinus miliaris. The close tuberculation of the am- 
bulacra is decidedly in favour of this supposition; on the other 
hand there is not a single feature which points distinctly towards 
Str. drøbachiensis. In case this latter species were one of the 
parent species, one should expect to find something recalling its 
more important characters: the polyporous condition of the ambu- 
lacra, the peculiar globiferous pedicellariæ (the valves being without 
Vidensk. Meddel. fra den naturh. Foren. 1911. Bd. 63. 5 
