CESTODES 195 



walls, or may be subdivided into 2 portions, of which the hinder may have 

 the appearance of a separate sucker; a pseudoscolex may also take the 

 place of the scolex; uterus usually an extensive sac, which may occupy 

 the greater part of the segment with a ventral opening; pore for cirrus 

 and vagina either marginal or dorsal: 7 genera; in fishes. 



1. Abothrium van Beneden. Suckers shallow ; a cylindrical pseudo- 

 scolex may be present in place of the scolex, the hinder margin of 

 which is prolonged backwards so as to project over the strobila; seg- 

 mentation of hinder part indistinct; cirrus and vaginal pores marginal, 

 that of uterus medium: 3 species. 



A. rugosum (Batsch). Length 25 cm. or more; breadth 4.7 mm.: 

 in the intestine of the cod; often common. 



2. BoTHRioCEPHALUS Rudolphi {Dibothrium Diesing). Scolex elon- 

 gate with rather weak suckers; no accessory suckers; segmentation 

 often indistinct; neck not present; uterine opening midventral; common 

 genital pore for cirrus and vagina middorsal: about 4 species. 



B. lacinatus (Linton). Body 15 cm. long, 4 mm. broad in the 

 middle, tapering towards hinder end ; segmentation distinct, the posterior 

 margins of the proglottids projecting backwards, making the margin of 

 the strobila serrate : in Tarpon atlanticus. 



Order 2. TETRAPHYLLIDEA. 



Scolex with 4 bothria, which vary much in form, being either stalked 

 or not and with or without hooks and accessory suckers; a pseudoscolex 

 may replace the scolex; segmentation distinct; cirrus and vagina open on 

 the margin; no uterine pore; yolk glands paired: 4 families and about 

 30 genera; in selachians, and also in other fish, amphibians, and reptiles. 



Key to the families of Tetraphyllidea here described: 



Oi Hooks present at the forward end of each bothrium .... 1. Onchobothriidae 

 02 No such hooks 2. Phyllobotheiidae 



Family 1. ONCHOBOTHRIIDAE. 



Hooks of various shape present in the anterior rim of the bothria; 

 bothria either sessile or with short stalks; accessory suckers usually 

 present ; the segments usually detach themselves before sexual maturity : 

 in spiral valve of selachians; 9 genera. 



1. Calliobothrixjm van Beneden. Bothria elongate, each being 

 divided by 2 transverse septa into 3 divisions of unequal size and with 

 either 1 or 3 small accessory suckers and 2 or 4 simple hooks: several 

 species. 



C. verticillatum (Rudolphi). Length up to 15 cm.; length of ter- 

 minal segment about 3.5 mm., width 1.7 mm.; a 3-lobed accessoiy sucker 

 and 4 hooks in front of each bothrium; body very slender, resembling 



