OF MKnrS.E MADE BY WILLIAM KEITH BROOKS. lM 



Genus DACTYLOMETRA L. Agassiz, 1862. 

 Dactylometra quinquecirrha L. Agassiz. 



Pelagla quinquecirrha, DESOR, E., 1848, Proc. Boston Soc. Nat. Hist., vol. 3, p. 76. 



Dactylometra quinquecirrha, AGASSIZ, L., 1862, Cont. Nat. Hist. U. S., vol. 4, pp. 125, 166. AGASSIZ, A., 1865, North Amcr. 

 Acal., p. 48, fig. 69. HAECKEL, 1880, Syst. der Medusen, p. 518. FEWKES, 1882, Bull. Mus. Comp. Zoul. at Harvard 

 College, vol. 9, No. 8, p. 293, plate I, figs. 2^-28, 38, 39. BIGELOW, 1890, Johns Hopkins Vniv. Circulars, vol. 9, No. 80, 

 p. 65. AGAPSIZ, A., AND MAYER, 1898, Bull. Mus. Comp. Zool. at Harvard College, vol. 32, p. i, plates i-i i, 33 figs. 

 HARGITT, 1904, Bull. U. S. Bureau of Fisheries, vol. 24, p. 69, plate 7, fig. 2. HARGITT, 1905, Journal Exper. Zool., vol. 2, 

 p. 575 (variations). VANHOFFEN, 1906, Nordischcs Plankton, Nr. n, p. 50, fign. 13-14. 



Bathyluca Solaris (damaged and regenerating specimen r), MAYER, 1900, Bull. Mus. Comp. Zool. at Harvard College, vol. 37, 

 p. 2, plate i. 



Chrysaora, BIGELOW, R.P., 1880, Johns Hopkins Univ. Circulars, vol. 9, No. 8, p. 66 (brackish-water variety from Chesapeake 

 Bay). 



Adult medusa. Bell nearly hemispherical, 170 to 190 mm. in diameter. Numerous 

 small, wart-like clusters of nematocysts thickly scattered over the exumbrella, especially 

 abundant at aboral apex where they appear as little hemispherical projections above the 

 general surface; near the margin they are elongate in shape, while at the margin itself they 

 are again hemispherical as at the apex. 8 marginal sense-organs, 40 tentacles, and 48 marginal 

 lappets. The marginal sense-organs are set within niches between the lappets, 4 being pcr- 

 radial in position and 4 interradial; these niches are protecied above by a small web between 

 the lappets. A ciliated, pit-like depression extends downward from the surface of the ex- 

 umbrella immediately above each sense-organ. The sensory-club projects slightly down- 

 ward and contains a distal, entodermal mass of crystalline concretions but no ocellus. The 

 entodermal core of the sense-club is hollow and its lumen is connected with the general 

 gastrovascular space of the medusa. 



There are 5 tentacles between each successive pair of sense-organs. 3 of these tentacles, 

 the primary and secondary, arise from the clefts between the lappets, but the other 2 (tertiary) 

 are generally found to spring from the under or subumbrella side of the ocular lappets; for 

 even in very large medusa? the ocular lappets exhibit but a slight notch adjacent to the ter- 

 tiary tentacles; in fact, the tertiary tentacles do not usually make their appearance until 

 the medusa is about 130 mm. in diameter and the lappets remain undivided until the medusa 

 is mature, although Hargitt shows that this is subject to great individual variability. Thus 

 in immature medusas of large size there are usually but 24 tentacles and 32 marginal lappets, 

 and the animal is in the "Clirysaora stage." I believe, also, that they often mature in this 

 stage and never reach the Dactylometra condition. 



The primary and secondary tentacles are very long and flexible while the tertiary ten- 

 tacles are only a few millimeters in length. In like manner the lappet-clefts of the primary 

 and secondary tentacles are deep and the lappets almost as long as they are broad; while 

 the lappet clefts of the tertiary tentacles are mere shallow notches in the contour of the lappets 

 adjacent to the sense-organs. Mouth-opening cruciform, in center of subumbrella, at extremity 

 of a 4-cornered oesophagus and surrounded by 4 mouth-arms or palps, which when fully 

 extended are about 7 or 4 times as long as the bell-diameter. The 8 free edges of the mouth- 



J r D O 



arms are complexly crinkled and highly flexible. The central stomach occupies a wide lentic- 

 ular space in the midst of the bell and gives rise to 16 simple, radiating pockets, 8 in the 

 tentacular and 8 in the rhopalar radii. These pockets are completely separated one from 

 another by 16 radiating septa which join the upper and lower walls of the umbrella cavity 

 together. The tentacles are hollow throughout the greater part of their length and their 

 entoderm is ciliated as is that of the stomach itself. 



The gonads are contained in 4 interradially situated, entodermal infoldings of the wall 

 of the subumbrella, and their position is marked by 4 deeply sunken, subgenital pits. The 

 genital organs are provided with numerous, simple, unbranched gastric cirri which project 

 inward into the stomach-cavity. There are two sets of radial muscle-fibers; the principal set 

 is found in the 16 septa between the gastric pouches, and alternating with these in position 

 are 16 strands in the exumbrella, 8 of which lead outward to the sense-organs and 8 to 

 the primary tentacles. 



Color quite variable. In some individuals the disk is pink, in others yellow with a 

 bluish opalescence. The exumbrella is thickly sprinkled with yellow-ocher colored nettlmg- 

 warts and there are 16 radiating stripes of reddish color upon the exumbrella in the radii of 



