HOLOTRICHA 563 



stome near posterior extremity; macroniicleiis round or sausage- 

 shape, central; a micronucleus; contractile vacuole posterior; 

 commensal in mantle cavity of various marine mussles. Many 

 species. 



A. mytili (Quennerstedt) (Figs. 18; 255, d, e). Oval; dorsal sur- 

 face convex, ventral surface concave; dorsal edge of peristome 

 curves around the cytostome; peristomal floor folded and pro- 

 truding; longitudinal ciliary rows on both surfaces; 3 rows of long 

 cilia on peristomal edges ; macronucleus sausage-form ; a compact 

 micronucleus anterior; 52-74;u by 20-38/^; Kidder (1933) found it 

 in abundance in the mantle cavity of Mytilus edulis at Woods 

 Hole and New York. 



A. isseli Kahl (Fig. 255, /). Pointed at both ends; 70-88^ by 

 31-54/x; Kidder (1933) observed it abundantly in mantle cavity 

 of the solitary mussel, Mediola mediolus, Massachusetts and New 

 York, and made clear its conjugation and nuclear reorganiza- 

 tion. 



Genus Eupoterion MacLennon et Connell. Small ovoid; slightly 

 compressed; cilia short, in longitudinal rows; rows of long cilia in 

 peristome on mid- ventral surface and extends posteriorly, making 

 a half turn to left around cytostome ; small conical cytostome lies 

 in postero-ventral margin of body; contractile vacuole terminal; 

 large round macronucleus anterior; a micronucleus; commensal. 



E. pernix M. et C. (Fig. 156, a). 46-48 ciliary rows; 6 rows of 

 heavy peristomal cilia; 38-56yu long; in intestinal contents of the 

 mask limpet, Acfnaea persoria; California. 



Genus Ancistrina Cheissin. Ovoid; anterior end attenuated; 

 peristomal field along narrow right side; 15-18 ciliary rows paral- 

 lel to peristomal ridges; cytostome right-posterior, marked with 

 oral ring, with a membrane and a zone of membranellae ; right 

 ridge of peristome marked by 2 adoral ciliary rows; macronucleus 

 anterior, spheroidal; a micronucleus; commensal. 



A. ovata C. (Fig. 256, b). 38-48|U by 15-20ai; in mantle cavity 

 of molluscs: Benedictia hiacalensis, B. Umneoides and Choanom- 

 phalus sp. 



Genus Ancistrella Cheissin. Elongate; ends rounded; ventral 

 surface less convex than dorsal surface; 16-17 longitudinal ciliary 

 rows; cihation uniform, except anterior-dorsal region, bearing 

 bristle-like longer cilia; 2 adoral ciliary rows on right of peristome, 

 curved dorsally behind cytostome; contractile vacuole posterior; 



