THE NAUTILUS. 97 



deposit is interglacial between the early and late Wisconsin 

 invasions. A paper covering this point is in preparation. 



EXPLANATION OF FIGURES, PLATE VII. 



1-3. Planorbis parvus Say. Owasco Lake, N. Y. X9 

 4-6. Planorbis parvus urba-nensis Baker, new variety. X9 



7. Planorbis altissimus Baker, young. X9. 

 8-10. Planorbis altissimus Baker, new species. X7. 



MOLLUSKS INFESTED WITH PARASITIC WORMS. 



BY FRANK C. BAKER. 



While carrying on biological work for the New York State 

 College of Forestry at Oneida Lake in the fall of 1917, many 

 animals were examined to ascertain the degree of parasitation 

 by worms. The hosts studied included fish, birds, batrachians, 

 reptiles, and mollusks. Among the latter many interesting 

 cases occurred, both of infestation and absence of infestation, 

 the degree of infestation varied from none to fifty per cent. 

 Of the twelve species examined, five were without trace of 

 parasites and seven were infested in varying degrees. It is 

 noteworthy that none of the Amnicolidae or Valvatidae were 

 parasitized, and that no worms were found in the small 

 Planorbes (parvus and hirsutus). Of those infested, five are 

 fresh water pulmonates. The examinations were carried on 

 under the direction of Dr. H. S. Pratt, of Haverford College. 

 The table below indicates the species infested and the degree 

 of infestation. All are trematode worms the species of which 

 have not yet been determined. 



Bythinia tentaculata 17 examined ; no worms. 



Amnicola limosa 20 examined ; no worms. 



Valvata tricarinata 20 examined ; no worms. 



Planorbis parvus 3 examined ; no worms. 



Planorbis hirsutus 1 examined ; no worms. 



Planorbis antrosus 2 examined ; 1 with cercariae, 1 without. 



