256 



MR, H. A. BAYLIS AND LT.-COL. CLAYTON LANE ON 



Key to Genera of Gnatliostoniiiife. 



A. Head-bulb fuvnisbed witb transverse cuticular ridges 



having sharp, backwardly-projecting edge's, but 



witliout hooks Tanqua. 



B. Head-bulb armed v^'ith transverse rows of recurved 



hooks. 



a. Body unarmed JEchhiocepJialus {-p. 27S). 



h. Body partially or wholly armed with backwardly- 



directed spines Gnathostoma (p. 291). 



TANQUA* R. Blanehard, 1904. " 



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



„ „ Stossich (1896, p. 52). 



Heterak'is (in part) v. Linstow (1904 «, p. 97). 

 Cteiiocephalmf v. Linstow (1904 p. 102). 

 Tanqua R. Blanciiar*d.(1904, p. 478). 

 Tetradenos v. Linstow (1904 6, p. 30J ). 



(1906, p. 173). 



This genus is characterized by having the large cuticular 

 head-bulb unarmed, 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 furtiier work. 

 Thus the lips are definitely lateral, and the statement formerly 

 made to the contrary (following the erroneous orientation of 

 von Linstow) is withdrawn. 



The lips are curiously asymmetrical, each being twisted slightly 

 towards the dorsal or ventral side, in such a way 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 interlock with those of the 

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

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

 stomach. 



The heaxl-bulb is divided by longitudinal indentations into 

 either two (a dorsal and a ventral) or four (submedian) 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 the forms which have only two 

 swellings, two ballonets are contained in each. 



* For generic diagnosis, see p. 258. 



t Not CtenocepJialus Kol., 1857 (dipteron). 



