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



In a discussion in connection with Mesonema pensile, Browne 

 (1904, p. 734) says: "The stomach is quite rudimentary and 

 is practically absent, as its lower wall is only about 2 mm. in 

 length, so that the mouth must always remain wide open." This 

 is not a necessary conclusion. I have seen the lower wall of the 

 manubrium of .'-/. coerulescens Br. contract to such a size and 

 present every appearance of being then in its normal permanent 

 condition: and I have also seen the same manubrium extend 

 readily and the wide mouth narrow and completely close by a 

 constriction above the oral fimbriations. 



Since the character on which Eschscholtz based his separation 

 of Aequorea and Mesonema is no longer considered adequate for 

 the purpose, the foregoing facts, taken in connection with the 

 admirable observations of Claus, would appear to argue conclu- 

 sively for the abandonment of M< sum ma, along with the no more 

 happily conceived Bhegmatodes and Polycanna. 



Aequorea coerulescens (Brandt). 



Mesonema (Zygodactyla) coerulescens, Brandt, 1835, p. 21; 



Brandt, 1838, p. 360, pi. 5. 

 Zygodactyla run nl< sn us, A. Agassiz, 1865, p. 108. 

 Mesonema coerulescens, Haeekel, 1880, p. 228. 



Umbrella thick, three times as broad as high, with a central. 

 broad swelling into the gastric cavity. Manubrium with a very 

 bi'oad base and about 60 oral fimbriations; its wall highly con- 

 tractile, mouth readily closed. Tentacles more numerous than 

 the radial canals, which number about 120. Velum narrow. 

 Gonads along nearly the entire length of the radial canals. 

 Bases of tentacles a bright blue, umbrella faintly bluish. 



Diameter may exceed 190 mm. 



Distribution. — Taken at the surface, in June and July, in the 

 vicinity of San Diego (Ace. Nos. 999. 1357, 1379). Mertens 

 obtained the type specimens about 1600 miles to the west of San 

 Diego. I met with it at Unalaska Island, in May, 1906. 



The northern specimens were larger than those taken by 

 Mertens. The San Diego individuals are much smaller, respec- 

 tively 4 mm.. 15 mm. and 55 mm. in diameter. In the last speci- 

 men there are but 9(1 radial canals, with indications of a some- 



