102 



CCELENTERATA 



to the velum ; length 6 mm. : common from Vineyard Sound to Gulf of 

 St. Lawrence in 8 to 30 fathoms. 



2. HYBOCODON Agassiz. Trophosome: polyp large, solitary, with a 

 well-defined perisarc and hydrorhiza; hydranth with a basal and 2 distal 

 whorls of filiform tentacles; just within the base of the former medusae 

 are budded off: 2 species. 



H. prolifer Agassiz (Fig. 167). Orange-colored hydroids 4 cm. high, 

 with longitudinally striated perisarc which is annulated just below the 

 hydranth; medusa hemispherical and asymmetrical, with 5 medidional 

 orange-colored bands at maturity and with 1 to 3 long marginal ten- 

 tacles, from the thick base of which secondary medusae bud : on rocks in 

 clear water from Vineyard Sound to Massachusetts Bay; not common. 



3. EcTOPLEUBA Agassiz. Trophosome : hydroid like Tubularia, being 

 indistinguishable when without gonophores. Gonosome: free medusae, 



Fig. 167 Fig. 168 Fig. 169 



Fig. 167 Hybocodon prolifer (Mayer). Fig. 168 Ectopleura ochracea (Hargitt). 

 Fig. 169 Turritopsis nutricula (Mayer). 



rather elongate, with 2 or 4 tentacles from the base of which lines of 

 nematocysts extend on the surface of the bell to its apex : 3 species. 



E. ochracea A. Agassiz (Fig. 168). Medusa about 3 mm. in height 

 with a large manubrium and 8 longitudinal bands of nematocysts on 

 exurabrella: Cape Cod to South Carolina; common. 



FAMILY 9. DENDBOCLAVIDAE. 



Trophosome: colony branching, with an elongate hydranth at the 

 end of each branch bearing 18 to 20 short filiform tentacles scat- 

 tered over it. Gonosome: a free-swimming medusa produced below 

 the hydranth: 2 genera. 



1. TURRITOPSIS McCrady. Hydroid form as above; medusa hemi- 

 spherical, with 8 to 70 equidistant tentacles; 4 reddish gonads: 1 species. 



T. nutricula McCrady (Fig. 169). Medusa 4 to 5 mm. in diameter: 

 Cape Cod to Florida; often common. 



