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No. 1. — Studies from the Newport Marine Laboratory. Commu- 
nicated by ALEXANDER AGASSIZ. 
XLI, 
On Dactylometra. 
By ALEXANDER Agassiz AND ALFRED GOLDSBOROUGH MAYER. 
Tux genus Dactylometra belongs to the Pelagidæ. At the present 
time there are four genera of this family known, and they may be dis- 
tinguished as follows : — 
(1) Pelagia, 8 tentacles, 16 marginal lappets. 
(2) Chrysaora, 24 tentacles, 32 marginal lappets. 
(3) Dactylometra, 40 tentacles, 48 marginal lappets. 
(4) Melanaster, 24 tentacles, 48 marginal lappets. 
Thirteen species of Pelagia and eight of Chrysaora are known, and 
they are found distributed among all of the great oceans of the world. 
There are only two species of Dactylometra, and they are found along 
the Atlantic coasts of North and South America. The genus Mela- 
naster is represented by but one species, M. Mertensii (L. Agassiz, Cont. 
Nat. Hist. U. S., 1862, Vol. IV. pp. 126, 166). It was described and 
figured by Brandt,! and is found in the North Pacific. 
The genus Dactylometra consists of Pelagidæ with 40 tentacles (3 
large and 2 small ones between each successive pair of marginal sense 
organs), and with 48 marginal lappets (6 between each successive pair 
of sense organs), 
In Dactylometra quinquecirra the bell is high, being almost hemi- 
spherical in shape. In mature medusæ there are five tentacles between 
each successive pair of marginal sense organs (Figs. 2-4, 6). Three of 
these tentacles, the primary and secondary (I, II, Il, Fig. 6), arise from 
the clefts between the lappets, and the other two, which we will call 
tertiary tentacles (LIT, III, Fig. 6), are generally seen arising from the 
1 Brandt, J. F., 1838; Mem. Acad. d. St. Pétersbourg, 6 Série, Tom. IV. p. 
885, Pls. XVI. and XVII. 
XXXII — NO. l. 
