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



readily Lost, may be as numerous as tentacles. Gonads narrow, 

 almost entire length of radial canals from margin. Ring' canal 

 yellow-green; bases of tentacles purple; edges of lips with a 

 single row of delicate purple spots. 



Largest 45 mm. in diameter. 



Distribution. — In numerous surface hauls off San Diego. 

 May-July. 



Fig. 4. — Mitrocoma discoidea. Slightly enlarged. 



The cirri vary greatly in number, being- rather more numer- 

 ous in the young. Medusae with 32 tentacles may have two cirri 

 between adjoining tentacles, though usually but one. In well- 

 grown individuals they are usually fewer in number than the 

 tentacles, and in many adults almost entirely wanting. 



The statocysts vary much in number, but never exceed sixty 

 and are usually nearer twenty. Occasionally two are found side 

 by side, dividing between them the usual number of statocysts, 

 apparently a result of fission. 



Gen. Tiaropsidium, n. gen. 



With 8 open statocysts, each with an ocellus at its base; with 

 two kinds of tentacles; without marginal cirri and gastric ped- 

 uncle. 



Maas (1905) has called attention to the fact that the existing 

 species of Tiaropsis are not of equal value. T. diademata Ag., 

 T. multicirrata Sars and T. Davisii Browne are characterized by 

 tentacles of but one kind. T. mediterranea Metsch., T. punctata 

 Mayer, T. rosea Ag. & M., Maas' species (which he identifies 

 provisionally with T. rosea) and the San Diego species are all 

 characterized by tentacles of two kinds, four or eight large and 

 a varying number of much smaller, more or less rudimentary 

 tentacles between them. 



