474 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



bodies ; in the older part of the colony quite largely double, occasion- 

 ally seen with seven divisions (Figure 19). Annulations above each 

 hydrophore divide the stem into nodes, others at base of branches and 

 occasionally elsewhere. Hydranths large with rounded hypostome and 

 twenty to thirty tentacles. 



Gonosome. Colonies dioecius. Gonothecae sessile at the axils of 

 hydrophores, sometimes found arising from hydrophores. 



Female gonotheca ovoid, flattened, with a short pedicel-like base, 

 one side open for two thirds its length, the edges of the opening form- 

 ing similar compound curves (Figure 18). The blastostyle extends up 

 around the opposite side, curving toward the opening. The develop- 

 ment of the eggs is accompanied by the breaking down of the tissue 

 between them and the opening. 



Male gonotheca (Figure 20) cylindrical and unusually slender, trun- 

 cate, and tapering to- 

 ward base, often marked 

 by an irregular encir- 

 cling groove somewhat 

 wavy in outline, one 

 third the way from the 

 base. 



Halecium marki (new 

 species). Figures 21-23. 



The creeping stolons 

 of this species form a 

 network over the Sar- 

 gassum and to a less 

 extent cover the bases 

 of some of the large 

 Bermuda hydroids. 



Trophosome. Colonies 

 are commonly one and a 

 half to three millimeters 

 high (Figures 21, 23). 

 A thick layer of spher- 

 ical, unicellular algae 

 extending through the 

 coenosarc of the entire 

 colony colors it green. A colony begins its growth as a single hydro- 

 phore arising from a stolon. Its structure, like other hydrophores, is 

 typically that of a cylinder ; it is three times as long as broad, with a 



Figures 21, 22. HaJecium marki. 



Figure 21. Colony (X GO). 

 Figure 22. Female gonotheca and hydranths 

 (X76). 



