442 POLYPI. VAGINATT. 



cles elongated. Inhabits fresh waters, under the leaves of aqua- 

 tic plants. Lam. ii. 108. 



SECTION VII. 



Polypiferous masses either free, isolated, and floating in the 

 water, or fixed and agglomerated in cellular masses compos- 

 ed of one substance on aquatic bodies ; polypi with nume- 

 rous tentacula, but not completing the circle round the mouth. 



The polypi of this section inhabit fresh and chiefly running waters. 



1. Fixed upon other bodies. 

 Gen. 64. ALCYONELLA, Lam. 



Polypiferous mass incrusting, thick, convex and irregular, com- 

 posed of an aggregation of vertical subpentangular tubes, 

 open at their summit ; polypi elongated, cylindrical, with fif- 

 teen or twenty straight tentacula disposed around the mouth 

 on one side at their upper extremity. 



A. stagnorum, Lam. (Alcyomumfluviatile, Brug.) Polypi forming a 

 mass of crowded irregular tubes, with a cylindrical cavity, obscure- 

 ly pentagonal at the opening. Ponds and springs Lam. ii. 102. 



Gen. 65. SPONGILLA, Lam. 



Mass fixed, polymorphous, irregular, cellular, composed of mem- 

 branous subpiliferous laminae, forming unequal, diffuse cells, 

 without order ; gelatinous and free granules in the cells. 



S.friabilis, Lam. Sessile, convex, obsoletely lobulated, fibrous with- 

 in ; fibres longitudinal, branched. Inhabits ponds in Europe. 

 Lam. ii. 100. 



S. ramosa, Lam. Sessile, branched ; branches elongated, roundish, 

 unequal, lobulated. Europe in ponds and lakes. Lam. ii. 100, 



2. Free andjloating in the water. 



Gen. 66. CRISTATELLA, Lam. 



Globular, gelatinous, free, with the surface covered by short 

 thick polypiferous tubercles ; summit of each tubercle inclos- 

 ing a polypus, of which the extremity is divided into two re- 

 tractile branches, arched and furnished with pectinated ten- 

 tacula ; mouth placed at the union of the tentacular branches. 



C. vaga?is, Roesel. Stagnant or running waters Lam. ii. 97 



Gen. 67. DIFFLUGIA, Lam. 



Body very small, gelatinous, contractile, inclosed in a testa- 

 ceous tube ; anterior part projecting beyond the tube, and 

 extending irregularly from one to ten tentacular arms ; sheath 

 oval or subspiral, truncated and open at the base, aggluti- 

 nating grains of sand at its external surface. 



D. protce'iformis, Lam. Europe on aquatic plants. Lam. ii. 95, 



