Protozoa (1)1(1 Ilotifcrd at Jlavaud, III. 337 



ing a more or less circular area ; five claw-like ventral styles 

 and five straight anal styles ; three long caudal setae at the 

 posterior extremity. 



74. S. mytilus Ehrbc. 



This species seems to avoid the open water, as it did not 

 occur in the towings, although it was not uncommon in oc- 

 casional shore collections among vegetation in June and 

 again in December. 



Section Peritricha. 



Family VORTICELLID^. 



Subfamily Urceolarin^. 



Trichodina Ehrbg. 



Free-swimming, more or less short-cylindrical, elastic and 

 flexible, especially the peristome end, which bears a well- 

 developed adoral zone ; posterior end forming an adhesive 

 disc, bearing a complicated attachment-ring of radiating 

 structure which is encircled by a posterior ciliary wreath, 

 used in creeping and swimming, margin of disc forming a 

 thin transparent edge. Parasitic on the surface of Hydra 

 and other invertebrates. 



75. T. pediculis Ehrbg. 



Frequent on Hydra rirtdls, in towings from Dogfish Lake 

 (substation L) in April. 



Subfamily VORTiCELLiNiE. 



SCYPHIDIA Duj. 



Not forming colonies ; individuals elongate-cylindrical, at- 

 tached by a posterior disc which does not bear a ring of 

 cilia ; peristome moderately well developed. Parasitic upon 

 mollusks. 



76. Scyphidia sp. 



A species of this genus was observed on the siphonal 

 papillae of Unio parvus, but was not determined. 



