HELMmTH PARASITES OF BIRDS — DENTON AND BYRD 163 



Specimens No. 36759 and 36760 from the robin, No. 37114 from the 

 mockingbird, and No. 37113 from the brown thrasher have been depos- 

 ited in the helminthological collection of the United States National 

 Museum. 



We agree with Travassos (1944) in considering L. Tnonenteron to 

 be very closely related to L. ohliquum (Travassos, 1917). The two 

 forms, however, can be distinguished readily by the length of the 

 cecum. In all the present specimens the cecum terminates well in 

 advance of the posterior end of the body, usually at the junction of 

 the middle and posterior body thirds, while in L. ohliquwm it termi- 

 nates just short of the posterior end. There is also a slight but con- 

 sistent difference in the size of the eggs. Since the North American 

 hosts of L. monenteron., with the exception of the kingbird (reported 

 by Ishii), are all nonmigratory birds or species in which migration is 

 confined to movements within the continent, and since certain definite 

 anatomical differences are observed, we are of the opinion that L. 

 monenteron and L. obliquum should be retained as separate species 

 until more is known concerning the life history and geographic dis- 

 tribution of the two forms. 



LUTZTREMA MICROSTOMUM, new species 



Figure 34, e, f 



Diagnosis. — Body of sexually mature specimens (fig. 34, e) semi- 

 transparent, elongated-slender, 3.00 to 4.95 mm. long by 0.19 to 0.46 

 mm. wide in region of vitellaria, tapering abruptly in preacetabular 

 region and more gradually toward posterior end. Cuticle thin, 

 aspinose, with small conical, retractile, sensory papillae visible on 

 lateral margins of preacetabular region. Oral sucker subterminal, 

 small, 0.07 to 0.13 mm. m diameter, preceded dorsally by a prominent 

 liplike projection. Acetabulum relatively large, 0.14 to 0.23 mm. in 

 diameter, muscular, cup-shaped with fairly deep lumen (fig. 34, /), 

 situated about one-tenth of body length from anterior end. Ratio of 

 diameter of oral sucker to acetabulum 1 : 1.75 to 1 : 2.80. Pharynx 

 slightly wider than long, measuring 0.03 to 0.05 mm. long by 0.03 to 

 0.06 mm. wide. Esophagus very thin-walled, slender, approximately 

 0.14 mm. long. Cecum slender and thin- walled, passing either to right 

 or left of anterior testis, between testes, and between posterior testis 

 and ovary, then continuing posteriorly in more or less wide undula- 

 tions to near body middle, where it terminates. Excretory pore 

 terminal. Excretory vesicle thin-walled, narrow, tubular, extending 

 anteriad to level of anterior limits of vitellaria, where it receives two 

 common collecting tubules. Each common collecting tubule receives 

 an anterior and posterior main collecting tubule at level of intertes- 

 ticular zone. Genital pore median, located approximately midway 



