20 Sigurd Johnsen. 
semilunata. On the whole I agree with this description; the dif- 
ferences in my specimens can most likely be explained by the dif- 
ference in size from Hertwig’s, which only measured 60 mm.') 
The scale falls into three parts; a dome-shaped hollow socket iu 
the skin, a stem, which proceeds from it and carries a free, star- 
shaped plate. (Pl. II, figs. 9—13). There are variations in the 
shape and size of the stem and upper plate. A difference can be 
discerned between two types of scales, which are, however, connec- 
ted by transition stages. The one (PI. II, figs. 10—12) has a 
strong stem, oval in section; the longitudinal axis of the oval lies 
lengthwise to the body. The upper plate has strong points, which 
as a rule are unbranched. (Text-figs. 7&8). The other has a thin 
stem, which also has an oval section; the top piece is more deci- 
dedly plate-shaped, with flat, irregularly branched points. (Text-fig. 
9, pl. II, fig. 13). The greater number are of the latter type, 
while the strong type, under examination of the skin and slightly 
magnified, catches one’s eye; it is also less affected by a solution 
of potash, so that it is easier to keep it whole during preparation. 
Judging from Hertwig’s illustrations, this type seems to have 
predominated in his specimen, the upper plate has from 4 to 6 
single points (Hertwig, p. 14); the fact that his specimen was 
younger than mine, may have something to do with this; 
Hertwig, however, mentions that the scales, in regard to shape 
of stems and size and number of points on the top plates, showed 
some variation. 
In addition to the scales, the skin is also furnished with spines. 
On each side at the base of the dorsal and anal fin, there is a “ow 
of single-tipped backward pointing spines (PI. II, figs. 6—7): 
the row is continued a little in front of the fins. On my specimen 
with a total length of 177 mm. there are about 17 spines along 
the anal, 25 along the dorsal fin. Scattered over the body, especiailv 
on the hinderpart there are also spines, most of these having two 
tips. (PI. II, fig. 8). The caudal side keel is absent, but here there 
is a row of 4—5 dumpy spines. Hertwig does not mention 
any such spines; on the other hand, he has found some forms of 
i 
?) This is probably the smallest known specimen; as Hertwig has 
based his determination on the description and illustration given by Cuvier — 
& Valenciennes (of Astrodermus elegans), it is reasonable to suppose 
that young individuals of 60 mm. do not to any extent vary in their form 
from those of individuals of about 200 mm. 
