LIMNOCODIUM (cRASPEDACUSTES) SOWERBII. 355 
the four radial canals or the perradial tentacles are the longest 
and thickest. The quadrant which intervenes between every 
two of these carries, at nearly the same height above the margin, 
about thirteen shorter and thinner tentacles, while between 
every two of these three to five much smaller tentacles are given 
off from points nearer to the margin, and at two or three levels, 
but without any absolute regularity ; indeed, in the older ex- 
amples all regularity, except in the primary or perradial tenta- 
tacles, seems lost, and the law of their sequence ceases to be 
apparent. 
I could find no indication of a cavity in the tentacles : but 
they do not present the peculiar cylindrical chorda-like endodermal 
axis formed by a series of large, clear, thick-walled cells which 
is so characteristic of the solid tentacles in the Trachomedusse 
and Narcomedusae. Erom the solid tentacles of these orders they 
differ also in their great extensibility, the four perradial tentacles 
admitting of extension in the form of long, greatly attenuated 
filaments to many times the height of the vertical axis of the 
umbrella, even when this height is at its maximum ; and being 
again capable of assuming by contraction the form of short thick 
clubs. Indeed, instead of presenting the comparatively rigid and 
imperfectly contractile character which prevails among the Tra- 
chomedusse and the Narcomedusae, they possess as great a power 
of extension and contraction as may be found in the tentacles of 
many Leptomedusae (Thaumantidae, &c.) . These four perradiate 
tentacles contract independently of the others, and seem to form 
a different system. All the tentacles are armed along their 
length with minute thread- cells, which are set in close, somewhat 
spirally-arranged warts. 
“ The lithocysts or marginal vesicles are, in adult specimens, 
about 128 in number. They are situated near the umbrellar 
margin of the velum, between the bases of the tentacles, and are 
grouped somewhat irregularly, so that their number has no close 
relation with that of the tentacles. They consist of a highly 
refringeiit spherical body, on which may be usually seen one or 
more small nucleus-like corpuscles, the whole surrounded by a 
delicate transparent and structureless capsule. This capsule is 
very remarkable, for instead of presenting the usual spherical 
form, it is of an elongated pyriform shape. In its larger end is 
lodged the spherical refringeiit body, and thence becomes 
attenuated, forming a long tubular tail-like extension, which is 
continued into the velum, in which it runs transversely towards 
its free margin, and there, after usually bocoming more or less 
convoluted, terminates in a blind extremity. 
The marginal nerve-ring can be traced running round the 
