100 CCELENTEEATA 



HYDRACTINIA Van Beneden. With the characters of the family: 

 2 American species. 



H. echinata Fleming (Fig. 162). Colony 10 mm. high; reproductive 

 individuals without tentacles: usually on the shells of hermit crabs but 

 also on stones, fucus, piles, etc.; very common on Atlantic coast; Europe. 



H. milleri Torrey. Colony 5 mm. high; reproductive individuals 

 with tentacles: California. 



FAMILY 6. PODOCOBYNIDAE. 



Trophosome: like that of Hydractiniidae. Gonosome: free medusae 

 present, each with 4 radial canals and 4 or 8 or more marginal tentacles : 

 several genera. 



Key to the genera of Podocorynidae here described : 

 Oj Medusa with long tentacles, hydroid on Limulus, shells of hermit crabs, 



etc 1. PODOCORYNE 



a a Marginal tentacles of medusa rudimentary ; hydroid on Nassa. . .2. STYLACTIS 



1. PODOCORYNE Sars. Trophosome: like Hydractinia. Gonosome: 

 medusa globular with 8 or more rather thick tentacles : 11 species. 



P. carnea Sars (Fig. 163). Medusa very transparent, 3 mm. high, 

 with 4 marginal tentacles in the young and 24 to 32 in the adult; 



manubrium reddish with 4 oral tentacles: 

 hydroid on Limulus, crabs, rocks, etc. 



P. fulgurans (A. Agassiz). Medusa 1 

 mm. high, hemispherical, with 8 marginal and 

 4 oral tentacles; manubrium buds off young 

 medusae: North Carolina to Massachusetts 

 Bay ; common ; often brightly phosphorescent. 

 2. STYLACTIS Allman. Trophosome: col- 

 ony consisting of very long, slender hydranths 

 rising from a reticular base. Gonosome : a 



sporosac in the European species, but in the 

 Fig. 163 Podocoryne car- A -^i T 



nea (Mayer). American a medusa with rudimentary ten- 



tacles: several species, 2 American. 



S. hooperi Sigerfoos. Hydranths 20 mm. long with 18 to 25 ten- 

 tacles; medusa globular, 1 mm. in height with 8 rudimentary, marginal 

 and no oral tentacles and borne on specialized hydranths, just below the 

 tentacles; no ocelli: Long Island and Vineyard Sounds, on Nassa 

 obsoleta. 



FAMILY 7. PENNARIIDAE. 



Trophosome: colony regularly branching; hydranth with a basal 

 whorl of 10 to 12 filiform tentacles and also a number of short knobbed 



