PROCEEDINGS OF THE NATIONAL MUSEUM. 197 



iminediately distal of the ])oucli. The changes in the genital system must 

 be left for some one to study who can preserve fresh material for this pur- 

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

 while several eggs are contained in each cai)sule in D. 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), contorfa and D. 

 viadai/d.scarkm.si.s, each capsule containiug but one egg. The ova are 

 about SO /.' in diameter and possess two ( t) surrounding membranes. 



The segments are all broader than long, variations being found 

 between 0.r)(> nun. broad by 4 /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 I>. sahnoni. As specific 

 name I have proposed J)avainea retractilis, referring to the retracted 

 condition of the suckers found upon all the heads exandned, 



Tlie material at hand does not warrant further description, ])ut from 

 the data given the following diagnosis is proposed: 



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

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

 much broader than long; segments vary from 0.50 mm. broad by 4 /i long 

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

 Head measures 0.37 to O.GS mm. broad by 0.3G to 0.43 mm. long. Ee- 

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

 booklets 12 /( long, about 40 to 00 hooks in each row. kSuckers meas- 

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

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

 arrange themselves regularly in rows, about 75 diagoiml rows coming 

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

 are estimated for each sucker, i^eck is short or absent, strobilization 

 beginning almost immediately back of the head. Longitudinal canals 

 at first very distinct, veuti'al canal lateral of dorsal canal. Genital 

 aulage 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 CO /< broad; 

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

 40 yu; a single egg in each egg capsule. 



Host. — One of the cottontail rabbits {Lepns arizotuv) by A. K. Fisher; 

 development not known. 



Types. — Diagnosis based upon four strobiLe with heads, and several 

 fragments; Bureau of Animal Industry Cestode series ]^o. 1180 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 11. Blanchard. 

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

 University; collection of Zschokke(Brde). All poorly preserved; tech- 

 nique, alchohol and hiematoxylin or acid carmine. 



Geographical distribution. — Nevada, bj^ A. K. Fisher. 



