214 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvii. 



amount of water in the body; for, if ttie specitic g-ravityof the l^illing 

 or preserving medium is \evx different from that of water, distortion 

 will occur. 



To kill expanded it is necessar}^ first to narcotize. Chloral hydrate 

 is used, added slowly in crystals until the poh^pides do not react to 

 touch. To preserve in the natural form, the animals ma}^ be plunged 

 directl}' into -i per cent formaldeh^^de (formalin, 10 per cent). 



The classification of fresh- water Brj'ozoa has been in a state of great 

 confusion owing to the great variability in the form of the colony. 

 The form of the colony depends very largely upon external factors, 

 such as food supply, form of substratum, and crowding. The stato- 

 blast has a form that is quite independent of external factors, and upon 

 it, consequently, great stress is laid in systematic work. The form of 

 the statoblast is, however, not wholly uncorrelated with that of the 

 stock, so the form of the stock is to be considered. In the following 

 classification that proposed by Kraepelin^' has been adopted entire, 

 although it does not conform to the writer's judgment in all particulars. 



A LIST OF ALL FRESH-W \TER BRYOZOA HITHERTO FOUND IN THE 

 UNITED STATES AND THE LOCALITIES WHERE THEY HAVE BEEN 

 OBSERVED. 



Subclass 1 .— ENDOF»ROCT A. 



This subclass comprises chiefl}' marine species, the only exception 

 being TJrnatella gracilh^ which was first described from the neighbor- 

 hood of Philadelphia, but which also inhabits the Mississippi Valley. 



Family PEDICP^LLINID.E. 



URNATELLA Leidy. 

 URNATELLA GRACILIS Leidy (1851). 



Stock consisting of a basal plate, from which there usually arise two 

 segmented stems terminating in the polypide. More rarely one or 

 more than two stems arise from the disc. 



Habitat. — Running water. 



DUtr'ilnitlonJ' — Schuylkill River under low-tide mark below Fair- 

 mount dam, Philadelphia, 1S51-1ST0, Leidy; *canal at Fairmount, 

 near Philadelphia, 1884, Potts (Leidy, 188J:), 1890, Potts and C. B. D.; 

 Scioto River, Ohio, Lea (Leid}^, 1883, p. 6); * Illinois River at Havana, 

 Illinois, Station E (middle of river), August, 1895 (Kofoid, 1898). 



The specimens from the Illinois River contrast with those from 

 Fairmount in the profuseness with which the}^ form lateral buds. 

 (Plate V, fig. 1.) 



« Die Deutschen Siisswasser Bryozoen, 1887. 



&An asterisk T)ef ore a locality name indicates that specimens from the locaUty have 

 been examined by the author. 



