AGASSIZ. NATURAL HISTORY OF THE UNITED STATES. 357 
Stomolophus is a new genus, which, of all Rhizostomes, appears 
to come nearest to the Monostomidce. Our knowledge of its single 
species is still very imperfect, for Professor Agassiz informs ns that 
he has “ only twice had an opportunity of seeing it, and, in both 
instances, under the most unfavourable circumstances.” 
Polyclonia frondosa is the Medusa frondosa of Pallas, and is 
identical with the Cassiopea frondosa of Lamarck and Eschscholtz 
{not of Tilesius). Professor Agassiz describes the structure of the 
mature zooid, with the aid of two excellent plates, and notes, like¬ 
wise, some interesting facts as to its habits :— 
“ This Medusa is one of the most singular Acalephs I know, both on account of 
the different aspects it presents in different attitudes, and on account of its habits. 
It is quite common upon the reef of Florida; I have seen immense numbers at Key 
Largo and at Key West, and occasionally at other points along the reef, and yet it 
is hardly ever seen near the surface of the water. This is owing to its habit of 
groping in the coral mud, at the bottom of the water, where thousands upon 
thousands may be seen crowded together, almost as closely as they can be packed 
upon the bottom, at a depth of from six to ten feet. When disturbed they do not 
rise, but crawl about like creeping- animals, now and then only flapping their 
umbrella, like other Discop horse.” 
The remarks contained in the text on the mutual relations and 
limits of the more noticeable families and genera among the Disco- 
phorce are best perused by way of commentary to the long Tabular 
View, in which a very complete classification of the whole order is 
brought forward. Its several families are therein arranged under 
three primary groups, or sub-orders, of which one, Semceostomece, 
is typical, and includes the monostome Phanerocarpce. The two 
remaining sub-orders are aberrant, one being constituted by the 
Phizostomece, while the other, LLaplostomece , contains the Charybdeidcs , 
AEginidee and Lucernariadce. No description or figure of any 
American species belonging to the Maplostomece is given. 
Order DISCOPHOMI. 
Sub-order I.—RHIZOSTOMEiE, 
Eamily 1 . — Rhizostomuele. 
Rhizostoma, Guv. 
Stomolophus, Ag. 
Stylonectes, Ag. 
Mastigias, Ag. 
Himantostoma, Ag. 
Cato stylus, Ag. 
Rhacopilus, Ag. 
Toxoclytus, Ag. 
Melitea, Per. Sf Les. 
Thysanostoma, Ag. 
Evagora, Per. fy Les. 
Eamily 2.—Leptobrachida:. 
Leptobrachia, Pr. 
Eamily 3.—Cassiopeid^. 
Cassiopea, Per. fy Les. Stomaster, Ag. 
Crossostoma, Ac/. Holigocladodes, Pr. 
2 b 2 
