VI. Some abnormalities in Asteroids and Ophiuroids. 
(Plate IV). 
In the course of my studies on Echinoderms I have now and 
then come across some more or less remarkable instances of abnor- 
malities, well deserving to be described, but I have always post- 
poned publishing anything about them, until more material had 
been collected. I may now take this occasion to publish here 
the description of the cases of abnormalities which I have brought 
together, as I shall probably otherwise not have the opportunity 
to do so- for several years to come. 
That such abnormalities are really more than mere curiosities, 
needs scarcely be emphasized. Jackson has recently, in his 
"Phylogeny of the Echini”, shown that very interesting general 
Considerations may be derived from similar abnormalities in the 
Echini. The same will probably be the case with the abnor- 
malities in the other groups of Echinoderms. It is, however, not 
my plan to enter here on a discussion of the probable meaning of 
these abnormalities. I intend only to give a simple description of 
the cases, leaving the discussion of the problems connected there- 
with for some future occasion. 
Meristic variation in the number of rays is of rather common 
Occurrence in both Asteroids and Ophiuroids. I have observed a 
not inconsiderable number of cases, and several cases have been 
recorded in literature; especially 4- or 6-rayed specimens of species 
which are normally 5-rayed appear to be not seldom occurring. On 
the present occasion, however, these cases are left out of considera- 
tion, this note dealing only with abnormal branching of the rays. 
The cases recorded in the older literature have been collected 
by W. Bateson in his "Materials for the study of variation” 
(1894, p. 440) and by Hamann in ""Bronn”!). It is quite a number 
for the Asteroids, while for the Ophiuroids no such cases are recorded. 
") Bronn. Klassen u. Ordnungen des Thier-Reichs. Echinodermen. II. 
Die Seesterne. 1899 (p. 737); IIL. Die Schlangensterne 1901 (p. 894). 
Vidensk. Meddel. fra Dansk naturh. Foren. Bd. 65. 16 
