256 MR. II. A. BAYLIS AND LT.-COL. CLAYTON LANE ON 



Key to Geneva of Gnathostoniinpe. 



A. Head-bulb f'uniished witli transverse cnticular ridges 



having sharp, backwardly-projecting edges, but 



without hooks Tanqua. 



B. Head-bulb armed with transverse rows of recurved 



hooks. 



a. Body unarmed Echinocephalus (p. 273). 



h. Body partially or wholly armed with backwardly- 



directed spines ... Gnathostoma (p. 291). 



TANQUA* R. Blanchard, 1904. 



Ascaris (in part) v. Linstow (1879, p 320). 



Stossich (1896, p. 52). 

 Heterakis (in part) v. Linstow (1904 a, p. 97). 

 Gteiiocephalus f v. Linstow (1904 a, p. 102). 

 Tanqaa R. Blanciiard (1904, p. 478). 

 Tetradenos v. Linstow (1904 6, p. 301). 

 (1906, p. 173). 



This genus is characterized by having the large cuticular 

 head-bulb vxnarmed, but marked with coarse and very distinct 

 transverse striations, having their posterior edges projecting so 

 as to give the outline of the bulb a more or less serrated appear- 

 ance in optical section. 



A former brief account given by one of us (Baylis, 1916) of 

 this genus requires some correction in the light of further work. 

 Thus the lips are definitely lateral, and the statement formerly 

 made to the contrary (following the erroneous orientation of 

 von Linstow) is withdra,wn. 



The lips are curiously asymmetrical, each being twisted slightly 

 towards the dorsal or ventral side, in such a wa}^ that the teeth 

 of the middle lobes cross each other like the blades of a pair of 

 scissors. The dorsal and ventral lobes of each lip do not, as was 

 formerly supposed, bear each a single tooth, but each is bilobed 

 on the inner surface so as to form two teeth. There are thus 

 five teeth on each lip, and these intei'lock with those of the 

 opposite lip, giving a very close bite, which enables the animal 

 to obtain a lirm grip of the tissues of the wall of its host's 

 stomach. 



The head-bulb is divided by longitudinal indentations into 

 either two (a dorsal and a ventral) or four (submediari) portions. 

 In the interior of the bulb are contained the four ballonets with 

 delicate membranous walls, the cavities of which are in com- 

 munication with those of the four cervical sacs. When the 

 head-bulb is divided into four swellings, each swelling contains 

 one of the ballonets ; while in tlie forms which have only two 

 swellings, two ballonets are contained in each. 



* For generic diagnosis, see p. 258. 



t Not Ctenocephalvs Kol., 1857 (dipteron). 



