IQQ CCELENTERATA 



Hydractinia Van Beneden. With the characters of the family: 

 2 Anierieaii 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. PODOCOKYNIDAE. 



Trophosome : like that of Hijdractiniidae. 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 : 

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



^ ' . 1. PODOCORYISE 



02 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: 

 y A hydroid on Limulus^ crabs, rocks, etc. 



...••• '■■■/ /liif P- fulgurans (A. Agassiz). Medusa 1 



\V ^^^^c^ll'i/M ^^^^' ^^^S'^^' ^hemispherical, with 8 marginal and 

 1 iVl ■•■■'V^'^'l^^ w/m1 ^ ^^'^^ tentacles ; manulorium buds off young 



\\ml^'^lf^^%Mimli medusae: North Carolina to Massachusetts 

 Vlii//- If '^^^'wJ/M ^^^' ' ^^^""^^^^ ' ^^*®" brightly phosphorescent. 



^|[l' '•■ ii /////fffM 2. Stylactis Allman. Trophosome: col- 



^^^M^^^^^w/// ony consisting of very long, slender hydranths 



^^^te^Pi:;?^^ rising from a reticular base. Gonosome: a 



^^^^^^'^^^ sporosac in the European species, but in the 



^'^' ^n'l^^XuyerT" '''''*' American a medusa with rudimentary ten- 

 tacles: several species, 2 American. 

 S. hooperi Sigerfoos. Hydranths 20 mm. long Avith 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. PENNAEIIDAE. 



Trophosome: colony regularly branching; hydranth with a basal 

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



