OBSERVATIONS ON POLTZOA. 



225 



3.5 



9x15 



upon small sticks and twigs in the fresh water of Mystic 

 Pond.* 



Variety b grows in long lines — rarely branching — upon 

 the surfaces of boards, and invariably solitary; the poly- 

 pides arranged sometimes 

 in one row, but oftener 

 in clumps of from two to 

 twenty heads, of all sizes 

 (PI. 9, figs. 1, 2). The 

 lower portions of the cells 

 are merged in the main 

 branch, the breadth of the 

 invaginated fold , when 



.1 1 • -1 • ^11 Fig. 17, a, a, front and back views of same 



tne pOlypiCle is lUlly ex- specimen from x\Iystic Pond; 6, side view of 



panded, is less, and the- ^^°*'^^^' ^'^^^^'^^'^^ ^^"^ ^^'^^^ ^°"'^- 

 polypide can be more fully evaginated than in any other 

 species (vide PI. 9, fig. 3.) When contracted, the cells 

 project but slightly above the branch. Viewed from 

 above, a branch is very like the variety of P. vesicularis 

 depicted in figure 18. It has been found only in Fresh 

 Pond. 



Variety c occurs upon flat pieces of tin and other broad 

 surfaces in the brackish waters of Mystic Pond. The 

 colonies differ from those of variety b in their diffuse and 

 closely crowded branches, forming a dense gelatinous 

 carpet. The statoblasts measured between .266 m. m. by 

 .366 m. m., and .383 by .566 m. m. In equal parts from 

 8 by 11 to 9 by 15, and 10 by 16 to 11 by 15, 11 by 16 to 

 11 J by 16, and 11 J by 17. Tne annulus from f at the 

 ends and | at the sides, to f at the ends and ^]-g at the 

 sides. Found only in Mystic and Fresh Ponds, Cam- 

 bridge, Mass. 



Plumatella vesicularis Leidy.f 

 This species, previously described from the neighbor- 



* This Pond is divided by a dam so that the upper portion is wholly 

 filled with fresh water, while the salt tide enters the lower part, ren- 

 dering it quite brackish. 



t Proceedings Philadelphia Academy Natural Sciences, vol. 7, p. 192. 



COMMUXICATIONS ESSEX INSTITUTE, VOL. V. 30 APKIL, 1868. 



