NO. 1105. PROCEEDINGS OF THE NATIONAL MUSEUM. 197 



immediately distal of the pouch. The changes in the genital system must 

 be left for some one to study AV!IO can preserve fresh material for this pur- 

 pose. Gradually the entire median field becomes filled with eggs; 

 while several eggs are contained in each capsule in I), salmoni, the ar- 

 rangement in 7). retractilis, so far as could be judged from the poor 

 material, agrees more closely with that described for I), contorta and D. 

 madagaxcariensis, each capsule containing but one egg. The ova are 

 about 80 J.L in diameter and possess two (?) surrounding membranes. 



The segments are all broader than long, variations being found 

 between 0.56 mm. broad by 4 j.i long (anterior segments) and 3 mm. broad 

 by 0.24 mm. long. The distal segments are slightly narrower, but there 

 is not the sudden and distinct change seen in D. salmoni. As specific 

 name I have proposed Davainea rctractilis, referring to the retracted 

 condition of the suckers found upon all the heads examined. 



The material at hand does not warrant further description, but from 

 the data given the following diagnosis is proposed: 



Diagnosis. Davainea retractilis, Stiles, 1895. Strobila 105 mm. or 

 more long by 3 mm. broad, with about 1,000 segments, all of which are 

 much broader than long; segments vary from 0.56 mm. broad by 4 /,* long 

 (anterior segments) to 3 mm. broad by 0.24 mm. long (gravid segments). 

 Head measures 0.37 to O.G8 mm. broad by 0.36 to 0.43 mm. long. Ee- 

 tractile rostellum 80 // by 48 /./, armed with a double row of minute 

 booklets 12 /,/ long, about 40 to 60 books in each row. Suckers meas- 

 ure 0.2 by 0.14 mm., and may be completely retracted into the bead; 

 they are armed with numerous booklets arranged in rows; the roots 

 arrange themselves regularly in rows, about 75 diagonal rows coming 

 to each sucker, and 5 to 20 roots in each row ; about 500 to 700 hooks 

 are estimated for each sucker. Neck is short or absent, strobilization 

 beginning almost immediately back of the head. Longitudinal canals 

 at first very distinct, ventral canal lateral of dorsal canal. Genital 

 anlage appears about 1 mm. from the head, and is at first median; tes- 

 ticles arranged in two groups, one each side of the median line. Gen- 

 ital pores unilateral, cirrus pouch small, 0.12 mm. long by 60 /* broad; 

 vagina immediately distal to pouch. Eggs 80 // in diameter, inner shell 

 40 /^; a single egg in each egg capsule. 



Host. One of the cottontail rabbits (Lepus arizoncc) by A. K. Fisher; 

 development not known. 



Types. Diagnosis based upon four strobilse with beads, and several 

 fragments; Bureau of Animal Industry Cestode series No. 1189 is des- 

 ignated as type and deposited in the United States National Museum. 

 Paratypes distributed as follows : Collection of Bureau of Animal In- 

 dustry; Berlin Museum; Vienna Museum; collection of E. Blancbard. 

 Fragments to British Museum; collection of Parona (Genoa); Tokyo 

 University; collection of Zscbokke (Bale). All poorly preserved; tech- 

 nique, alcbobol and hseinatoxylin or acid carmine. 



Geographical distribution. Nevada, by A. K. Fisher. 



