T^NIOID CESTODES OF NORTH AMERICAN BIRDS. 



25 



pole terminating in a small globular expansion. Length of outer 

 shell, including processes, 120 to 125/x; central portion 50/* long by 

 38 to 40/* wide ; diameter of tubular processes 3 to 4/i, of globular ex- 

 pansion 10 to 17/1. Inside of the outer shell a 

 second thin, well-defined shell, spherical, 33 to 

 36/x in diameter. Oncosphere 26/i in diameter. 



Genus RHABDOMETRA Kholodkovski, 

 1906. 



(For generic diagnosis see p. 86.) 



RHABDOMETRA NULLICOLLIS, new species. 

 Figs. 15-22. 



This species has been found in the sagecock 

 {C entrocercus urophasianus) and in the sharp- 

 tailed grouse {Pedioecetes 'phasianellus colum- 

 hianus). The type-specimens (No. 6018, U. S. 

 Nat. Mus.) were collected from the first- 

 named host in Colorado. 



External anatomy. 



-4 



Fig. 14. — Liga beasili- 

 ENSis : Egg. 



The various specimens of this species which 

 have been studied measured 50 to 100 mm. in 

 length by 2 to 2.5 mm. in maximum width. 

 The head (figs. 15, 16) is obtusely pointed 

 anteriorly, 560 to 650/i wide, about 360/i thick, 

 and 280 to 330/i long, without rostellum. The suckers are 110 to 160/t 

 in diameter. A neck is absent, segmentation beginning immediately 

 behind the head. The segments are at first of the same width as 

 the head, or slightly wider, and gradually increase in width, finally 

 decreasing again at the posterior end of the strobila. The first seg- 

 ments are less than 20/t in length, sexually active segments measure 

 330/t in length by 1.25 mm. in width, the largest segments measure 

 1.25 mm. in length by 2 to 2.5 mm. in width, and the final segments 

 2.8 mm. in length by 1.3 mm. in width. The posterior border of each 

 segment overlaps the anterior end of the following segment only very 

 slightly, and is but slightly wider than the anterior border, so that 

 the segments are nearly quadrate in shape. 



The sexual pores are irregularly alternate, located in the anterior 

 third of the segment. 



