THE NEMATODE FAMILY GNATHOSTOMID^. 



277 



backwards. The neck-papillje were not seen. Caudal papilla? 

 could not be detected, nor was the position of the vulva yet 

 visible. The cuticular striation is extremely line and indistinct. 



As regards the occun-ence and life-history of this species, it 

 seems fairly clear that it requires an intermediate host, in the 

 shape of a bivalve mollusc, for its transference into the alimentary 

 canal of its final host. Molin's original adult material was found 

 in Trygon hriicco in the Adriatic, von Linstow (in Shipley and 

 Hornell, 1904) states that it also occurs in T. juistinaca. The 

 larval stages are found encysted in the tissues of bivalves, usually 

 in the adductor muscle of the shell. Tlius they have been found 

 fairly frequently in the pearl-oyster (see Shipley and Hornell, 

 1904, pp. 101-102), and we have now recorded their occurrence 

 in Pinna sp. In tlie pearl-oyster the larvae are occasionally 

 found " entombed in the nacreous lining of the shell "' (Shipley 

 and Hornell, 1904), where their shape is said to be wonderfully 

 preserved. 



In addition to the bivalves, the trigger-fishes, Balistes mitis 

 and B. steUatics, are recorded by Shipley and Hornell (1904) as 

 hosts for the later larval stages. It is not quite clear whether 

 these fishes are rega.rded as a necessary second host of the parasite 

 or not. The species of Trygon are said to devour both the Balistes 

 and the oysters, but the presence of the worms in Balistes may 

 have been abnormal. In these fishes they were found not only in 

 the alimentary canal, but also in the peritoneum and connective 

 tissue, in which they were thought to buri-ow by the help of the 

 hea,d-bulb, which was seen in both inflated and deflated conditions. 



Specific Diagnosis. 



EcHixocEPHALUS UNCIXATUS Moliu, emend. Baylis and Lane. 



Head-bulb with six rows of hooks, each row containing from 

 40 to 50 hooks. 



For list of hosts, see p. 289. 



2. EoiiiNOCEPHALUS spixosissiMUS * (v. Linst., 1905). (Text- 

 figs. 25-29; PI. lY. figs. 17, 18.) 



Echinoce-phalus unciaatus (in part) Molin (1858, p. 154). 



„ (1861,p. 311,pl.xiii. 



figs- 5, 6). 



CheiracantJuis spinosissimiis v. Linstow, in Shipley and Hornell, 

 (1905, p. 54, pi., figs. 12, 13). 



This specific name was proposed by von Linstow for a form 

 having 30 to 33 rows of hooks on the head-bulb, each row 

 containing some hundreds of hooks. The host of the ty[)e- 

 specimens was Myliobalis aquila, from the Gulf of Manaar. 



* For specitic diagnosis, see p. 283. 



19* 



