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 tightl}^ 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 

 perihsemal caual 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 perihsemal 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 Ophinra Itevis 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 costosura, 

 showed a general structure very like that of Gorgonocephalus ; but, on 

 passhig from the true Astrophj-tous, a decided anatomical change was at 

 once manifest. 



A specimen of the rare Astrocnida isidis, from the " Blake " dredg- 

 iugs, 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 II. fig. G), 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, cither along the arms, or in the 

 interbi-achial spaces. The only vestige of such attachments was a stout 

 septum, such as is found in Ophiurans, lying outside the wall of the 

 mouth-sphincter, (/?<, and thus forming a closed ring-tube (inner peri- 

 hccmal canal). It may more propei'ly 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, 8, 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 ai'e not 

 connected with or surrounded by any bursa, but lie directly in the body 

 cavity, into which penetrate the genital openings. The genital organs 



