222 HYATT, 



with numerous rows of posterior retentor muscles. Sta- 

 toblasts with plain annulus, and rounded extremities. 



Plumatella diffusa Leidy. 



I found this species abundant in the ponds and brooks 

 near Cambridge and Baltimore. Those which inhabited 

 the brooks differed greatly from the pond varieties. The 

 first, or variety a, has distinct cells, with tough, brown 

 ectocyst, and the branches diffuse, and rarely adherent 

 (PI. 8, figs. 11, 12, 13). The pond varieties, or variety 

 5, were much denser growths ; the branches generally ad- 

 herent, the ectocyst colorless, and, in several specimens 

 from Mystic Pond (living in brackish water, associated 

 with Cordylophora), the branches were so closely packed 

 that the colonies formed thin, gelatinous sheets of consid- 

 erable extent, in which no branches could be traced from 

 above. The cells also had the hexagonal outline usually 

 ascribed to Alcyonella, and their lower portions were 

 more or less merged in the branch. 



The brook variety, or variety a, was generally keeled 

 and channelled, but this was an exceedingly variable char- 

 acter. Polypide was not examined. 



Statoblasts vary from .199 m. m. in breadth by .333 

 in length, to .249 in breadth by .349 in length. In equal 

 numbers they vary from 6 by 10 to 6 by 12, 6.5 by 11.5, 

 and 7.5 by 10.5. 



Here, again, as in other species, the transverse diam- 

 eter is increased steadily, while the longitudinal fluctuates 

 between 10 and 12. Annulus varies between f and ^ at 

 the ends, and between l^\ and [^ at the sides. 



6x12 7.5x10.5 



Fig. 14, a, a, a, side, front, and baolt views of one specimen; b, b, front and back 

 views of another, all from Mystic Pond, Mass. 



