128 MELICERTID^. 



COSMETIRA Forbes. 



A remarkable Hydroid Medusa, belonging to the genus Cosmetira of 

 Forbes, was brought home by the Anticosti Expedition. 

 Magdalen Islands, Gulf of St. Lawrence. 

 Cat. No. 371, Magdalen Islands, N. S., Anticosti Expedition. Medusa. 



Family MELIOERTIDiE Agass. 



Melicertidce Agass. Cont. Nat. Hist. U. S., IV. p. 349. 1862. 



GONIONEMUS A. Agass. 



Gonionemus A. Agass.; in Agassiz's Cont. Nat. Hist. U. S., IV. p. 350. 1862. 



Gonionemus has a general resemblance to Melicertum, but differs 

 from it by the shape of the ovaries and of the spherosome. The 

 spherosome is an oblate half-spheroid, cut from pole to pole ; the ova- 

 ries are in lobes alternating on the sides of the chymiferous tubes, and 

 extending their whole length, from the digestive cavity to the circular 

 tube ; the digestive cavity is long, and very flexible ; the tentacles are 

 numerous, large, and exceedingly contractile ; chymiferous tubes four 

 in number. 



Gonionemus vertens A. Agass. 



Gonionemus vertens A. Agass. ; in Agassiz's Cont. Nat. Hist. U. S., IV. p. 350. 1862. 



This Medusa was quite commonly found during the month of July, 

 swimming in patches of kelp. It at once attracted my attention by 

 its peculiar mode of moving. I could see these Jelly-fishes, with the 

 tentacles spread out to their fullest extent, sinking slowly to the bot- 

 tom, the disk turned downward ; the moment a blade of kelp touches 

 the disk, they stop, bend their tentacles like knees, and remain at- 

 tached to the sea-weed by means of their lasso cells (Fig. 197), which 

 are arranged m rings scattered thickly over the surface of the ten- 

 tacles ; after remaining attached in this way a moment, with their 

 tentacles extended and mouth turned upwards, they suddenly let go 

 their hold, turn upside do\\Ti, contract their tentacles (Fig. 198) to a 

 thu-d of their former length, and begin their upward movements by 

 means of short, rapid jerks, given by the sudden expanding and con- 

 tracting of the tentacles as they are violently thrown out from the 

 cavity covered by the veil. They keep up this rapid motion until they 

 reach the surface of the water , at the instant the upper part of the 



