76 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 55. 



tions and importance of the tapeworms as well as to distinguish them 

 from one another. The key does not cover the species in the family 

 Diphyllobothriidae. 



1. Head pi'ovided with two slit-like suckei-s, and segments with a rosette-shaped 



utei'us having a special aperture in the midveutral line for the discharge 



of eggs. Larvae in fish Diphyllobothriidae, p. 4. 



Head with four cup-shaped suckers 2. 



2. Follicular yolk glands in the lateral fields. Accidental in the dog. 



Ophiotaenia punica, p. 4. 

 Yolk glands in median field, never in lateral fields 3. 



3. Genital pore located on the ventral surface near the median line. Eggs In 



gravid segments, contained in a single tliick-slielled egg capsule. 



Mesocestoiiles lineatus, Mesocestoides litteratus 



(probably identical species), pp. 59, 61. 



Genital pore lateral. Eggs in gravid segments, contained in a uterus or in 



numerous egg capsules 4. 



4. Usually large forms. Genital pores irregularly alternate. Rostellum usually 



well developed and usually armed with a double crown of hooks, rarely with 

 a single ( ?) crown of hooks or unarmed. Suckers unarmed. Uterus with a 



median stem and lateral branches. Eggs thick shelled Taeniidae, 5, p. 5. 



Usually small forms. Genital pores single or double; if single, regularly or 

 irregularly alternate. Rostellum present or absent ; if present, armed with 

 one to numerous rows of hook.s. Suckers armed or unarmed. Uterus sac- 

 like and persistent, or a single or double uterus with one or several para- 

 uterine organs, to which the eggs pass in the final stage of development. 

 Eggs vnth thin, transparent shells Hymenolepididae, 19, p. 61. 



5. Strobila less tlian 1 cm. long and composed of a head and 3 segments, only 



one of the segments being gravid at a time. Lateral uterine branches 

 often quite indistinct. Yolk-gland globular. Larval stage an echinococcus 

 with thick laminated wall, and developing brood capsules containing the 



larval scolices Echinococcus granulosus, p. 56. 



Strobila at least several centimeters long and coruposed of a head and nu- 

 merous segments, from 10 to hundreds, with a number of segments usually 

 gravid at one time. Lateral uterine branches usually distinct, at least in 

 early stages of formation. Yolk gland posterior of ovaries and elongate or 

 triangular, with one side parallel to the posterior margin of the segment. 

 Larval stage a bladderworm with thin walls and never containing brood 

 capsules 6. 



6. Strobila without a neck and with a double circlet of many and very large 



hooks, the large hook over 300 ^ long, or with only a single circlet of hooks 

 (?). B!add(H■v;orn!^:, so far as known, with a small caudal bladder and 

 with a long seguu']ited structure connecting the bladder and head. Para- 

 sitic in Felidae 7. 



Strobila with a neck and with a double circlet of hooks, the large hook less 

 than 300 ji long. Bladderworms with a caudal bladder, a head and a mod- 

 erate-sized neck. Parasitic in Canidae 10. 



7. Rostellum with a single circlet of hooks of rose-thorn-shape. Reported from 



Lijvx lynx (Felis lijnx) Taenia monostephanos, p. 38. 



Rostellum with a double circlet of hooks, the large hooks over 300 [jl long — 8. 



8. Large hooks 60 to 74 in number; 320 to 355 fi long; the large hooks ar- 



ranged so as to form in effect 2 circlets of large hooks, being alternately 

 nearer to the center of the rostellum and farther from it. 



Taenia macrocystis, p. IS. 

 Large hooks not over 60 in number 9. 



