16 University of California Publications in Zoology. [Vol. 6 



one-fifth the distance to apical pole from margin, other cycles 

 successively nearer margin. Ocelli on bases of the tentacles of 

 the last two cycles. Manubrium, gonads and tentacles pale yel- 

 low; canals yellow, occasionally carmine. 



Full-grown individuals about 75 mm. high. 



Distribution. — Surface at La Jolla, California. Acq. No. 

 1279. California coast to San Francisco. 



This is one of the largest and most beautiful of the Hydro- 

 medusae. The closeness of its relationship to Polyorchis is shown 

 not only by the character of the gonads and occasional traces of 

 lateral branches of the radial canals distal to the gonads, but by 

 the presence of an individual in the collection with well-devel- 

 oped lateral branches on each radial canal between margin and 

 gonads, showing that this Polyorchis character may be perfectly 

 adopted by a sudden individual variation. Such a variation is, 

 however, exceedingly rare. It may be interpreted as the appear- 

 ance of a latent rather than a new character. 



The gastric peduncle is well developed in the smallest indi- 

 viduals (8 nun. high) in the collection. There is. however, a 

 gradual increase in its size with the growth of the individual 

 and a corresponding shortening and thickening of the manu- 

 brium, which is long and slender in the 8 mm. individuals where 

 it may project from the bell cavity. The general resemblance 

 to Polyorchis is especially striking in these young forms. 



In 1894. a single large individual was collected at the surface 

 in the harbor of Oakland. California, where Polyorchis penicil- 

 lata was formerly common. The U. S. S. Albatross obtained a 

 considerable number of large specimens in 1904 from Monterey 

 Bay, in dredge hauls from 19 to 86 fathoms. 



Fain. Mitrocomidae Haeckel, 18S0. sens. i m. 

 s< iis. I.ufi,, ,,hn Maas. 1905. 

 Leptomedusae with large open statocysts. 

 Metschnikoff (1886) obtained from the eggs of both Laodict 

 and Mitrocoma very similar hydroids with the characters of 

 Cuspidella Hincks. For this reason, he regarded both genera of 

 medusae as Lafoeidae, the family in which, according to Hincks. 

 Cuspidella should be placed. Owing to the striking differences 



