BY T. HABVEY JOHNSTON AND O. W. TIEGS. 93 



5. A N c H y L o D I s c u s, n.gen. 



This genus is characterised by the occurrence of fear very large hooks on 

 the clinging disc, together with fourteen minor hooks scattered over it. Three 

 pairs of head-organs. Four eyes, the anterior pair farther apart than the 

 posterior. Pharynx large and rounded. Intestinal limbs end blindly. Vesieula 

 seminalis not highly dilated. Testis directly above ovary. Penis a simple 

 ehitinous tube. Shell-glands probably simply glandular thickening's of the walls 

 of the oviduct. Vitelline system very well developed. Egg of relatively enor- 

 mous size. 



Found, so far, only on the gills of Siluroid fishes in Queensland. 



Type species, Anchylodisnus tandani J. & T. 



Anchylodiscus tandani, n.sp. (Plate x., figs. 8, 9; xi., figs. 10, 11.) 



This pai-asite is rather small, but thick-set, measuring about .3 mm. in 

 length, .06 to .08 mm. in breadth. 



The head-end is indistinctly marked off from the remainder of the animal. 

 The disc (PL x., fig. 9), which is very prominent and fairly sharply marked 

 off from the body, is armed with four relatively vei-y large hooks, each slightly 

 bifurcated basally, the bases of each pair of hooks being joined by a simple 

 eross-bar. The edge of the disc is prominently lobed to form partial supports 

 for the laxger hooks. Fourteen minute hooks ai'e filso present. 



Of the body musculature the outer circular and delicate internal longitudinal 

 layers are visible. The longitudinal layer of the posterior end is strongly deve- 

 loped to form the musculature supplying the disc. 



Three pairs of head-organs are present. Anterior to the median pair, the 

 "head" possesses a pair of small but distinct lobes. The cephalic glands lie 

 laterally to the anteiior pair of eyes. 



The mouth appears to open ventrally, but could not be definitely observed. 

 The pharynx is prominent, its anterior portion lying immediately behind the 

 posterior pair of eyes. There is a definite oesophagus of moderate length. The 

 bifurcated intestine ends blindly. Unicellular glands are visible in the pharynx. 

 There is also a pair of prominent glands situated on either side of the oesop- 

 hagus. 



No trace of the excretory system could be recognised. Of the nervous sys- 

 tem, only the brain was visible, lying immediately between the eyes. The latter 

 are very lai-ge and prominent and are situated in the body parenchyma, im- 

 mediately below the body wall. Their arrangement differs from that of most 

 other Gyrodactylids in that tlie smaller anterior eyes are farther apart than the 

 posterior. 



The reproductive organs are of a rather simple type. The testis is elongated 

 and lies dorsally to the ovary, reaching from well in front to a short distance 

 behind it. The vas deferens arises from it laterally, passes in the dorsal region 

 of the body almost to the right side, then turns forward, inward and downward 

 to open in the middle line into a large, transversely-placed, renifomi vesieula 

 seminalis which lies close behind the pharynx. The more anterior portion of 

 the vas deferens undergoes a slight dilatation a short distance before the per- 

 manent vesieula. From the latter the vas deferens passes backward as a rather 

 narrow tube and opens into a small rounded bulbus ejaculaforius, lying at the 

 base of the cirrus. The latter is a simple ehitinous tube, bent almost into a 

 complete circle and opening immediately in front of the female aperture. 



