12. Basal portion of body much narrowed to form a slender stalk 



Pelmatohydra oligactis (Pallas) Brown Hydra 

 (Hydra fusca Linn.) 

 Body more uniform — Hydra Linn, (several species) 13. 



13. Tentacles, when extended, much longer than the extended body 



Hydra camea Agassiz Red Hydra 

 Tentacles shorter than the body; color whitish 



Hydra americana Hyman Common or Gray Hydra 

 (Hydra vidgans Pallas) 

 (Hydra grisea Linn.) 



14. Colony in a more or less spherical, flattened, triangular or ribbon -like 



mass; statoblasts (groups of cells set apart for vegetative reproduction) 

 with marginal, hooked spines; lophophore (crown of tentacles of each 

 animal of the colony) appearing divided, lyre-shaped or somewhat rc' 

 sembling a pair of wings 15. 



Colony somewhat lobed, branching or plant-like, sometimes forming a 

 conspicuous mass but often very small; statoblasts without hooked 

 spines or projections; lophophore lyre-shaped or circular 17. 



15. Colonies usually very small, somewhat triangular; usually on water 



plants; statoblasts oval, with several graduated, hooked spines or pro- 

 jections on each end, which spines usually bear two to eight hooks or 

 prongs distributed along the sides of the spines out to the ends; colony 

 capable of very slow motion; recently discovered near Philadelphia 

 and in Lake Erie and probably recently introduced into this country 

 Lophodella carteri (Hyatt) 

 (Lophopodella carteri (Hyatt) ) 

 Colonies usually large enough to be quite noticeable, sac-like or ribbon- 

 like; statoblasts more rounded, with one or two completely encircling 

 rows of marginal spines, which bear two or more hooks or prongs at 

 their ends 16. 



16. Colony flattened on the under side, long and narrow; with the power 



of extremely slow motion; becoming one-quarter of an inch by eight 

 inches; on twigs, the under sides of lily pads, etc.; statoblasts with a 

 double row of more than twenty-five marginal spines, some of which 

 have more than two hooks or prongs at the ends 



Cristatella mucedo Cuvier 

 Colony sac-like; incapable of moving; becoming extremely large; attached 

 to sticks, etc.; statoblasts with a single row of less than twenty-five 

 marginal spines, which have two prongs or hooks at the ends 



Pectinatella magnifica Leidy 



17. Lophophore with more than thirty tentacles and appearing divided, lyre- 



shaped or somewhat resembling a pair of wings 18. 



Lophophore with less than thirty tentacles in a circular arrangement 20. 



18. Colony somewhat glove-shaped, very small; on roots of duck-weed, on 



plant stems, etc.; mature statoblasts pointed or drawn out at each end, 

 with a brownish, cellular marginal ring 

 Lophopus cnstalhnus (Pallas) 

 Colony plant-like, sometmies small or sometimes forming a conspicuous 



57 



