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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 55. 



the body, rather completely fused at the segmental junctions so that 

 the segmental junctions are not clearly defined as they are in the 

 anterior four segments; maximum width of the body in segment 

 VII; segments V and VIII subequal; segmental margins of seg- 

 ments V to VIII broadly flattened forming a conspicuous shelf beyond 

 the thicker portion of (he body; segment IX greatly reduced, not 

 prominent in dorsal view; caudal sucker large, ventral, its width 

 in contracted specimens about equal to that of the head ; head large, 

 in contracted specimens exceeding the first two body segments in 

 size; head divided into two rather distinct units, the anterior being 

 slightly shorter than the posterior; lips two, each with a median 

 emargination ; dental formula 5-4 or 6-5, varying from 4-4 to 7-0 

 (see subspecies) ; major pharyngeal diverticula three, two dorsal and 

 one ventral ; each anterior nephridium opening to the outside through 

 a separate pore in segment III ; spermatheca in segment V, small and 

 simple, subglobose with a small dorsal tubular portion, not bifid; 

 testes in segments V and VI ; vasa deferentia from segments V and 

 VI joining the large atrium in segment VI; accessory sperm tube 

 present and well developed ; alimentary canal rather straight in seg- 

 ments I to V, maximum enlargement in segment V, intestine more or 

 less displaced (usually to the right) in segment VI depending upon 

 the state of the enlargement of the reproductive organs in that seg- 

 ment; intestine forming two rather distinct loops in segment VII, 

 decreasing rapidly in diameter from segment VII to the anal open- 

 ing on the dorsal surface of segment IX ; largest specimen examined 

 was strongly contracted and measured 2.0 mm. in length. 



The two lots of specimens of this species, from Eugene, Oregon, 

 and Sequallitchew Lake, Washington, form a continuous series 

 through the several types of dental formulae from 4-4 to 7-6, but 

 none of the Washington worms have less than 6-5 teeth and the 

 majority of the Oregon worms have 5-4 teeth, the maximum den- 

 tition of this series being 6-5. Correlated with this difference in dental 

 formulae the Oregon sj)ecimens have upper jaws in which the two 

 short median teeth of the " a " order are not equal in length, and 

 the Washington worms have upper jaws with subequal " a " teeth. 

 These two lots therefore have been regarded as representing two 

 subspecies, X. oregonensis oregonensis and X. orego7iensis pecti- 

 natus. The variation in teeth is shown below. 



Table 3. 



