724 Proceedings of the Boyal Irinh Academy. 



The Valencia specimens show that the Medusa has at first 

 four perradial tentacles, and that the four interradial tentacles 

 are of later growth. 



Phialidium cymbaloideum (van Beneden). 



Phialidium cymbaloideum, Browne, 1896, P. Z. S., p. 491, pi. xvii. 



In 1895, during April and May, a large number of specimens 

 were collected, and a series formed to show the development of 

 the Medusa from the earliest stage to the adult form. 



In 1896, from July to September, the Medusa was very 

 scarce. IN'early all the specimens belonged to intermediate 

 stages ; a specimen of the earliest stage was taken on August 

 28th. Early in November the intermediate stages were 

 abundant, but the Medusa was not taken in December. The 

 appearance of the young and intermediate stages in the autumn 

 shows that the Hydroid liberates Medusae in the autumn as 

 well as in the spring. 



In 1897, it first appeared in January and disappeared in 

 October. 



On January 27th early stages were taken, and on February 2nd 

 a large specimen, 7 mm. in diameter, which probably came from 

 the autumn stock of the previous year. Early in March 

 the earliest and intermediate stages were abundant ; a slight 

 decrease occurred in April, but during May and June the 

 number again increased, so that in July the Medusa became 

 very abundant, both intermediate and adult specimens being 

 present. After a rapid decrease in September the Medusa 

 finally disappeared in October. Apparently there was no 

 autumn brood as in the previous year. 



In 1898, the Medusa first appeared in March and disappeared 

 in October. It never became abundant at any time during the 

 summer. 



This Medusa is probably liberated from a Hydi'oid belonging 

 to the genus Campamdina, so that the abundance of the Medusa 

 and its first appearance depend upon the breeding activity of 

 the Hydroid. It is a very common British species, and may be 

 distinguished by its thick umbrella, and by the presence of only 

 eight marginal sense organs which have more than one otolith 

 in each. The youngest stage has four tentacles and four mar- 

 ginal sense organs ; but the presence of at least two otoliths in 

 each sense organ distinguishes this species from the young 



