64 THE AMERICAN MONTHLY [April, 



Analytical Key to the Sedentary Genera of the Fresh-Water Peritricha. 



A. Animalcules free-swimming; ciliary system an anterior wreath, with or without 

 a postero-terminal circle, and occasionally an equatorial girdle of locomotive 

 appendages. (Omitted for the present.) 



A. Animalcules permanently attached ; ciliary system one or more anterior wreaths 



of vibratile appendages; inhabiting fresh water (B). 



B. Animalcules illoricate (without protective sheath) (§). 

 B. Animalcules loricate (with protective sheath) (§§). 



B. Animalcules immersed within a gelatinous investment (§§§)• 

 § Animalcules sessile (a). 

 § Animalcules with a pedicle (c). 

 §§ Lorica erect (/). 



§§ Lorica decumbent; adherent by the flattened side (o). 

 §§§ Gelatinous sheaths solitary ..... Ofhionella, S. K. (Fig 22). 

 §§§ Gelatinous sheaths forming adherent or freely floating masses often visible to the 

 naked eye . ■ . . . . . Opkrydium, Ehr. (Figs. 23-25). 



a. Anterior border bearing cilia only {b). 



a. Anterior border bearing a hyaline, membranous funnel. 



Spirochona, Stein (Fig. 3). 



b. Body posteriorly attached by a sucker-shaped cup . Scyphidi'a, Duj. (Fig. 2). 



b. Body posteriorly attached without a sucker-shaped cup, Gerda, C. & L. (Fig. i). 



c. Pedicle without a contractile, muscular thread {d). 



c. Pedicle with a muscular thread ( /"). 



d. Pedicle simple (not branching) \e). 



d. Pedicle compound (branching) (/). 



e. Pedicle alwavs motionless, usually shorter than the body ; ciliary disc not one-sided, 



'Rhabdosiyln, S. K. (Fig. 4). 

 e. Pedicle motionless, short; ciliary disc one-sided, . Pyxidiitm, S. K. (Fig. 6). 



e. Pedicle springing backward when the zooid contracts, curved below, usually well 



developed, ..... Opist/tostyla, Stokes (Fig. 5). 



f. Pedicle simple (not branching) {g). 



f. Pedicle compound (branching) (/i). 



g. Zooids attached singly to the highly contractile pedicle, Vorticella, L, 

 h. Muscular thread interrupted at each bifurcation of the pedicle, 



Carchcsium^ Ehr 

 h. Muscular thread continuous through the main stem and the branches, 



Zoothamtiinm, Ehr, 

 i. Ciliary disc not one-sided, without a collar-like membrane, 



Episiylis, Ehr. (Fig. 10) 

 /. Ciliary disc one-sided; a small collar-like membrane below and to one side of the 

 disc, ........ Opercularia, Stein (Fig. 11) 



j. Lorica sessile (>t). 

 j. Lorica with a pedicle (/). 



k. Lorica with a movable, oblique valve, and an opposite bristle-like valve-rest below 

 the aperture within, .... Thuricolopsis, Stokes (Fig. 14). 



k. Lorica with an internal valve but no valve-rest, . Thuricola, S. K. (Fig. 13). 



h. Lorica with neither valve nor valve-rest («). 



/. With an antero-lateral, horny operculum, . . Pyxicola, S. K. (Fig. 16). 



/. With an antero-lateral, soft, fleshy operculum, Packytrocha, S. K. (Fig. 18). 



I. Without an operculum (wi). 

 m. Aperture of lorica permanently open when the zooid is contracted, 



Cothurnia, Ehr. (Fig. 15). 

 in. Aperture of lorica closed (valvular) when the zooid is contracted, 



Stylohedra, Kellicott (Fig. 19). 

 n. Zooid posteriorly attached to the lorica by numerous radiating processes, 



Siylocola, From. (Fig. 17). 

 ti. Zooid posteriorly attached to the lorica directly, or by means of a short pedicle, 



Vagitiicola, Lam. (Fig. 12). 



