No. 415.| MWORTH-AMERICAN INVERTEBRATES. 585 
Willia ornata McCr. (FIG. 49). 
Body of medusa bell-shaped or conical, with blunt apical projection ; 
marginal tentacles sixteen in mature specimens, arising from the terminals 
of the branched radial canals; pri- 
mary canals four in young specimens, 
which by repeated branching become 
sixteen, and the development of the 
tentacles follow the same course of 
development, appearing after the 
several divisions of the canals ; manu- 
brium rather stout and with lobed oral 
margins. Intermediate between each Fic, 49-— Wellia ornata McCr. 
(After A. Agassiz.) 
pair of tentacles an undulating line 
of nematocysts, ‘‘ knotted cords,”’ passes upward on the bell. Hydroid (?). 
(Adapted from McCrady’s description, Proc. Elliott Soc., Vol. 1, p- 149.) 
LEPTOMEDUS. 
As compared with the Anthomeduse, the Leptomeduse are generally 
flatter and more disk-like; the velum is usually smaller, and the texture of 
the bell is softer. Ocelli may or may not be present; otocysts may or may 
not be present ; the gonads are borne upon the radial canals. 
SYNOPSIS OF FAMILIES. 
I. THAUMANTID&. Ocelli present, but no otocysts; radial canals four 
or eight (rarely more), always simple and unbranched. 
II. CANNoTID#&. ‘Without either otocysts or ocelli; radial canals four 
or six, which are branched or pinnate. 
III. Eucopip#. Otocysts always present, eight or more ; ocelli usually 
absent ; radial canals usually four, simple and unbranched. 
IV. A:QquorIDA. Otocysts always present; radial canals numerous, at 
least eight, often a hundred or more, usually simple, rarely branched. 
Key to Genera. 
THAUMANTID. 
A. Radial canals four; marginal tentacles numerous, and with basal 
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B. Radial canals eight; marginal tentacles numerous, but without basal 
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