MUSEUM OF COMPARATIVE ZOOLOGY. 121 
It will be noticed that the genital openings are greatly distended, 
which shows that the animal can contract or expand them ; since, in 
other specimens, they were tightly shut and reduced to a small slit. 
The attachments of the stomach to the inner open angle of the mouth- 
frames are not so thick and muscular as in Gorgonocephalus, so that the 
perihæmal canal is flattened, instead of more or less erect, and rounded. 
Nevertheless there are the same ten radiating attachments respectively 
along the tops of the arms and the middle of the interbrachial spaces, 
dividing the body-cavity into ten compartments, which freely communi- 
cate at their inner ends by the perihæmal canal In the lining mem- 
brane of these compartments were found numerous fragments of 
microscopic lime network similar to that which exists in the walls of 
the bursa of Ophiura levis and Ophiocoma scolopendrina (Ludwig, loc. 
cit., Figs. 27, 28). It is these that, by their further growth, make the 
thin scales which clothe the wall of the bursa in Ophiothamnus vica- 
rius. 
A section of a species from an allied genus, Astrophyton costosum, 
showed a general structure very like that of Gorgonocephalus; but, on 
passing from the true Astrophytons, a decided anatomical change was at 
once manifest. 
A specimen of the rare Astrocnida isidis, from the * Blake " dredg- 
ings, afforded a chance to examine a branching star, like Astrogomphus 
in outward appearance, but resembling Trichaster in its few and widely 
spaced arm-forks. On making a vertical section (Plate IL. fig. 6), a 
curious and quasi intermediate structure was exposed. The stomach 
recalled Gorgonocephalus in that it was more or less pleated and pouched 
(St), and was firmly attached to the roof of the disk-wall; but it was 
Ophiuroid in being entirely free below, and partly so on its sides, hav- 
ing no radiating lines of attachment, either along the arms, or in the 
interbrachial spaces. The only vestige of such attachments was a stout 
septum, such as is found in Ophiurans, lying outside the wall of the 
mouth-sphineter, du, and thus forming a closed ring-tube (inner peri- 
hæmal canal). It may more properly be called an adhesion of the floor 
of the stomach to the wall of the mouth, where they are doubled over 
each other. Between the upper side of the stomach and the disk-wall, 
and on top and on either side of each arm, lie the ovaries, à, which con- 
sist of almost separated ovoid egg-clusters, rather more than 1 mm. in 
length, containing round eggs about .2 mm. in diameter. "They are not 
connected with or surrounded by any bursa, but lie directly in the body 
cavity, into which penetrate the genital openings. The genital organs 
