CONGDON. 



THE HYDROIDS OF BERMUDA. 



477 



Hydrothecae alternate, embedded in stem or pinna nearly to the 

 opening, separated by a considerable space from each other, cylindrical 

 and flattened laterally, the lower end tapering slightly, with no line 

 marking its union below and no diaphragm, the upper end bending out 

 at an angle of sixty degrees. The hydrothecae of the branches grow 

 from a pair of tubes on opposite sides of the stem. There are usually 

 three between successive pinnae 

 on one side, one of which is just 

 above the origin. 



The opercula of young hydro- 

 thecae have four, or occasionally 

 five, ridges, terminating in corre- 

 sponding projections of the edge ; 

 one abcauline, and the others 

 symmetrically placed. Opercu- 

 lum usually first ruptured at 

 centre. Four ragged lobes or a 

 rim may remain until maturity, 

 but they are more commonly lost. 

 Projections usually persist, be- 

 coming less distinct. Two or 

 three rings usually found below 

 the edge of old hydrothecae. 



Expanded hydranths trumpet 

 shaped, hypostome conical, ten- 

 tacles twenty to thirty. A blind 

 sack is attached to abcauline 

 wall of hydrotheca, from which 

 projects a transverse edge. 



Gonosome. Colonies dioecious. 

 Male and female gonothecae, aris- 

 ing from pinnae, externally simi- 

 lar, equal to five hydrothecae in 

 length (Figure 26). Theca hya- 

 line, cylindrical, distally truncate, 

 proximally constricted for one 

 fourth its length into a pedicel- 

 like base. Axis slightly curving, 

 markings of surface often very 

 faint, consisting of eleven longitu- 

 dinal ridges terminating in lobes along the distal margin, separated 

 by more faint parallel ridges and six or eight broad shallow circular 



Figure 24. Sertularella speciosa. 

 Colony with gonothecae (X li). 



