22 The MoUuscan Family Planorhidae 



were unsuccessful, although species of this genus are parasitized by other 

 forms of trematode worms. 



Aguayo (1938, p. 210) has summarized the species of snails used as 

 intermediate hosts by Schistosoma and other trematodes. Schistosoma 

 haematobium is shown to use a species of planorbid, 'Planorbis dufuorii' as 

 well as Bulinus and Physopsis. The Schistosoma mansoni intermediate 

 hosts include Ajroplanorhis boissyi, A. pfeifferi, A. sudanicus, Australorbis 

 glabratus, A. olivaceus, A. antiguensis, Tropicorbis centimetralis, and Dre- 

 panotrema cultratus. 



The liver flukes of the genus Fasciola parasitize certain genera of 

 Lymnaeidae [Radix, Pseudosuccinea, Fossaria, and Stagnicola) as well as 

 one Physa, P. cubensis. The large fluke of the Orient, Fasciolopsis buski, 

 which is closely related to Fasciola, uses only the small planorbids belonging 

 to the old genus Segmentina which now includes the groups Pohjpylis, Heli- 

 corbis, and Pingiella, true Segmentina not being found in the East. Four 

 species are listed as intermediate hosts, Planorbis coenosus { = Helicorbis) , 

 Segmentina hemaesphaenda {=Polypylis) , and \Seg)nentina sch)naken 

 and '*S. nitidella' which have not yet been examined for their anatomy and 

 hence their position is doubtful (probably Polypylis) . The value of cor- 

 rect specific identifications of the intermediate hosts of these trematode 

 worms is of- the first importance as has been clearly indicated by Ingles 

 (1933) in a study of the parasites of frogs. 



Elaborate studies have been made by Dr. E. C. Faust of the Depart- 

 ment of Tropical JVIedicinc in Tulane University, New Orleans, and by the 

 late Dr. William A. Hoffman of the School of Tropical Medicine of the 

 University of Puerto Rico, on various phases of the Schistosomiasis man- 

 soni problem in Puerto Rico, where the mollusk Aiistralorbis glabratus 

 (Say) (=Planorbis guadeloupensis Sowb.) is the intermediate host. For 

 these studies see Faust, 1933; Hoffman and Faust, 1934; and Faust, Jones, 

 and Hoffman, 1934. 



Papers by parasitologists in which molluscan hosts are mentioned are 

 numerous. A few are here indicated. Faust (1918) has observed cercariae 

 of four species in Helisoma trivolvis in Illinois and one species in Heli- 

 soma sidjcrenatum (not trivolvis, as stated) in ^Montana (Faust 1917). In 

 a list of the described cercariae of the United States ( 1919) Faust men- 

 tions two species of the family Planorbidae, Planorbis parvus (Gyraulus) 

 and Planorbis trivolvis (Helisomci) , as well as several Physidae and 

 Lymnaeidae which are known hosts. Fourteen species of cercariae infest 

 Helisoma trivolvis and three species occur in Gyraidus parvus. Miller 

 (1936) found Helisoma trivolvis from Illinois and Helisoma trivolvis 

 lentum (not lantum, typographical error) from Louisiana to be hosts of 

 many American cercariae. O'Roke (1917) found Helisoma trivolvis (prob- 

 ably the race lentum) carrying cercariae in Kansas, and McCormick 

 (1923) found Helisoma trivolvis and Gyraulus parvus to be infested in 

 Ohio. Ward (1918), in Ward and Whipple's Fresh-water Biology (pp. 365- 

 424), summarizes the cercarial stages of parasitic flatworms, gives keys 

 for the determination of the larval stages and indicates the species of 

 mollusks which have served as intermediate hosts. Physa, Lymnaea, and 

 Planorbis are listed, including many of the Planorbidae. However, this 

 text was compiled at the very beginning of studies on trematode life 

 histories on this continent. More recently there have been numerous de- 



