24 University of California Publications in Zoology [Vol. 16 



The type and eotypes are deposited in the collections of the proto- 

 zoological laboratory of the Departnaent of Zoology of the University 

 of California. One cotype slide is deposited in the United States 

 National ]\Iuseum. 



Giardia microti sp. nov. 



Diagnosis. — Length of body 1.83-2.47 transdiameters, widest 0.25- 

 0.35 of total length from anterior margin, slender tapering pos- 

 teriorly, parabasals slender, curved awl-shaped, usually oblique, 0.5 

 tran.sdiameter in length. Length 10-16 jx, transdiameter, 5-7 fi. Host, 

 Microtus californicus calif ornicns (Peale), in intestine from duodenum 

 to rectum. 



Description. — Body elongate pyriform in outline in dor.sal or 

 ventral view, with semicircular anterior outline, widest 0.25-0.35 of 

 total length from the anterior end towards the posterior margin of 

 the cytostome. The region posterior to this is tapering conical 32°- 

 55° with slightly concave, rarely convex sides. The cytosome {cyt., 

 fig. A) occupies the anterior 0.3-0.5 of the flattened ventral surface 

 and follows closely the anterior outline of the body somewhat more 

 than in G. muris. 



The organism is a binucleate somatella of usual Giardia type. The 

 two nuclei inuc, fig. 1) are ellipsoidal in the prophase, 2-2.5 /x in 

 length. 



Giardia microti has the same extranuclear organelles as other species 

 of the genus. The neuromotor apparatus consists of a rhizoplast 

 passing from the karyosome {intraniic. rhiz.) through the centrosome 

 (cent.) at the anterior pole of the nucleus, thence to the blepharoplast 

 (l. hleph.) of its side of the axostyle. From, or near the blepharoplasts 

 arise all of the flagella. Of these there are three pairs, bilaterally 

 arranged with respect to the major axis of the body. 



The antero-lateral flagellum {ant. lat. fl.) passes anteriorly within 

 the cytoplasm in a sweeping curve to the opposite side of the body, 

 meeting its mate of the opposite side in the anterior chiasma {ant. 

 chiasma), a node in the two fibers in the median plane, and runs thence 

 in the rim of the cytostome {intracyt. lat. fl.) parallel to the anterior 

 peristome as a somewhat thicker strand usually obscured by the 

 peristome, and emerges from a small basal granule {lat. has. gr.) as a 

 free flagellum {ant. lat. fl.) 



