224 HYATT, 



Remarks. I have collected variety a generally upon 

 broad surfaces in moderate currents or still water ; but 

 small colonies may occur upon twigs 

 and roots. In Tommy's Brook, vari- 

 ety b is associated with variety c of 

 F. regina ; while farther down the 

 brook, variety a is found in company 

 with variety b of that species. Jt is 

 « 2 2 s' evident here that the Alcyonelloid 

 Fig. 16, four varieties of Varieties of both spccics are due to 

 sMe!''''Thf outunei^coiT^^^ the actiou of the limited areas of 

 spend to those with similar oTowth aud extraordinary develop- 



letters in fig. 1.5, but their ^ „ , -, . "^ ■*■ 



thicljness is represented by mCUt 01 the reproductive pOWCrS. 

 tlie numbers below. In both rni • ^ -\ ' ±i i ^ 



figures n., a, are from Mystic i he Specimens louud 111 the orack- 

 pomij i^tror^F^£^ ish Water of the outlet of Great Pond 

 see Pond. ^^e Small coloiiics agreeino; in general 



character with the small-sized Fredericellffi, also found 

 there. Those in Mystic Pond belonged to variety b, 

 agreeing in all respects with the specimen of P. vesicu- 

 laris, diifusa, and vitrea, found together near the (mtlet of 

 the lower pond. Those from Fresh Pond belonged to 

 variety a, and were associated with variety a, F. regina, 

 variety b, P. vitrea, and variety a, P. vesicularis. The 

 general character assumed by the different species leads 

 at once to the supposition, as the only reasonable infer- 

 ence, that these varieties are the results of the association 

 of the different sjDCcies under the action of similar physi- 

 cal causes. 



Plumatella vitrea Hyatt. 



The coenoecia of this species are covered by colorless 

 gelatinous ectocysts, rather thicker than in any other of 

 the PlumatellEe, except the Alcyonelloid variety of P. 

 diffusa. 



Variety a has radiatory branches, and the cells are 

 more distinct than in variety b ; but the lower portions are 

 merged. in the common branch more than in the diffuse 

 form of P. vesicularis or diffusa. When contracted, the 

 cells are quite distinct and prominent. It is common 



