242 
Upon the whole the Asteroids appear to be more liable to produce 
abnormalities and meristic variations than the Ophiuroids, as is 
also pointed out by Verrill!). A few cases have been recorded 
since the publication of Hamann's work. Ludwig (Arktische 
Seesterne; Fauna Arctica. p. 470 (1900)) mentions a specimen of 
Pteraster militaris from Spitzbergen in which ,,ein Arm gegabelt 
(ist), wodurch das Exemplar unvollkommen sechsstrahlig geworden 
ist.” Michailovsky?) describes two cases of fusion of rays in 
Ctenodiscus crispatus, in which ,je zwei Arme einander betråcht- 
lich genåhert und auf eine gewisse Strecke hin gleichsam mit ein- 
ander verschmolzen sind.” Koehler ("Siboga” Ophiuroidea. I. 1904 
p. 64) mentions a specimen of Ophiomusium impurum, which has 
one arm bifurcated. Finally Verrill (Op. cit. p. 549) mentions 
a specimen of Asterias epichlora (Brandt), in which one ray is 
forked about at the middle. 
The cases, which I have to mention, are the following. 
Asterias rubens Linn. The specimen figured in Pl. IV, Fig. 1 
is remarkable through having a pair of symmaetrically arranged 
lateral arms on one arm, Nr. 2 to the right of the madreporite. 
The two abnormal arms are almost of the same size as the outer 
part of the arm, from which they proceed. One of the abnormal 
arms (the left in the figure) presents the interesting feature that 
the adambulacral spines on nearly the inner half of the arm åre 
regularly biserially arranged, while otherwise they are rather 
regularly alternating in this species. On the aboral side the colour 
of the abnormal arms is conspicuously lighter than that of the 
rest of the animal. On opening these arms I find that the coeca 
do not send branches into them; likewise it may be noticed that 
the genital organs do not continue into these abnormal arms. 
1) A..E. Verrill. Remarkable development of Starfishes of the North- 
west American Coast; hybridism; multiplicity of rays; teratology ; 
problems in evolution; geographical distribution. American Naturalist. 
XLIII 1909. No. 513 (p. 556). 
2) Echinodermen d. zoolog. Ausbeute d. Eisbrecher Jermaks im Sommer 
1901. Ann. Mus. St. Petersbourg. IX. 1904, p. 171. 
