346 JAMES F. GEMMILL 
other four originates in the region of the stomach or manubrium. 
Indeed, in the earliest stage of the Melicertidium medusa 
identified by Browne (4, p. 768) the gonads extended outwards 
from the stomach only along the proximal halves of the radial 
canals. 
The Leptomedusan Family Thaumantiadae, to which 
Melicertum and Melicertidium belong, contains other twelve 
typical genera. The hydroid stages of only three of these, 
viz. Thaumantias (Wright, 11), Laodicea (Metchnikoff, 8), 
and Dipleurosoma (Browne, 8), are known, and, curiously 
enough, they all possess complete thecae. In having a rudi- 
mentary theca Melicertum recalls the Anthomedusan Peri- 
gonimus, while Melicertidium having no theca is in line with 
Hutima (Campanopsis) and Tima, which are members of the 
Leptomedusan Family Kucopidae. Dr. James Ritchie com- 
pares the general facies of the Melicertidium hydranth to that 
of Halecium. ‘The just liberated medusa of Melicertidium 
resembles that of Podocoryne carnea except in having 
a slightly shorter manubrium and no oral tentacles. It is 
evident that on the borderland between the Antho- and the 
Leptomedusae there are numerous forms which, whether in 
their hydroid or their medusoid stages, exhibit features charac- 
teristic of better-defined members of either group. 
I have to thank the Trustees of the Carnegie bequest for 
uw grant m aid of the expenses of this investigation, and the 
staff of the Millport Station for help in obtaining material and 
rearing the young medusae. 
REFERENCES. 
1. Agassiz, A.—‘‘ North American Acalephae ”, * Cat. Mus. Comp. Zool. 
Harvard ’, ii, 1865, p. 130, figs. 202-4. 
2. Brooks, W. K.—*‘ On the Life-history of Kutima and on Radial 
and Bilateral Symmetry in Hydroids ”’, * Zool. Anz.’, Bd. 7, 1884. 
3. Browne, E. T.—‘ Fauna and Flora of Valencia Harbour i SOG: 
Roy. Irish Acad.’, ser. iii, vol. 5, 1898-1900, p. 696. 
“A Report on the Medusae found in the Firth of Clyde ”’, * Proc. 
Roy. Soc. Edinburgh ’, 1905, p. 72. 
4. 
