274 



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



the dorsal and ventral lobes of the lips, so that each lip bears 

 some 20 teeth altogether. 



The head-bulb forms a continuous ring surrounding the base 

 of the lips; it is never, in the species hitherto met with, divided 

 externally into two or four swellings, as in Tanqua^ though it 

 still contains the same four ballonets connected with the cervical 

 sacs. The latter sometimes end in a little button-like appendage 

 (text-figs. 30, 33, a). 



The size of the hooks on the head-bulb, the number of rows, 

 and the number of hooks in each roAv, show considei'able variety, 

 and afford useful specific characters. 



The body is smooth, as in Tcmqua, the cuticle being, as a rule, 

 finely striated transversely. The neck-papillai are rather pro- 

 minent. Molin's statement (1861) that the anus is lateral is 

 entirely erroneous. The excretory pore is very inconspicuous, 

 and is always to be found at about the same level as the cervical 

 papillfe. 



The tail of the male is coiled ventrally, and is provided with 

 slight cuticular alae, into which a series of paired caudal papilla? 

 project. Of these there are always eight pairs, as in Tanqua, but 

 tlie arrangement of the pairs difiers somewhat in the diff'ei'ent 

 species. One constant feature is the long space separating the 

 eighth or most anterior pair from the rest. 8ome of the papillae 

 are rather large, with a swelling at the base recalling that seen 

 in Tanqiia, but never so well-developed. The spicules are very 

 characteristic. They are tubular and usually rather long and 

 slender, the left spicule being apparently always a fraction of a 

 millimetre longer than the right. Instead of the broken, externaJ,. 

 rasp-like markings seen on the spicules of Tanqua, we find in 

 EcMnocephalus an irregular transverse striation, which only 

 breaks up into a rasp-like pattern near the tip. The markings 

 appear to be internal, the outer surface being smooth and trans- 

 parent. The tip of the spicules consists of a thickening of the 

 smooth outer layer only, and may be sharply pointed or somewhat 

 blunt in different species. 



The tail of the female is short and bluntly rounded at the tip. 

 The vulva is invariably situated near the posterior end of the- 

 body, within a very short distance of the anus. The long vagina 

 runs forward, and it seems to be characteristic of the genus that 

 it forms a single coil m its course before opening into the uterus. 

 The latter consists of a wide oblong egg-sac, which becomes very 

 voluminous in the gravid female, and two horns which run for- 

 ward from its anterior end. The ova have a finely granulated 

 surface, and are of a similar oval shape to those of Tanqua. 

 They do not contain fully-formed embryos when laid. 



The adults are found in the intestine (usually in the spiral 

 valve region) of sting-rays (Trygonidte and Myliobatidfe). There 

 is evidence that the development is indirect, requiring an inter- 

 mediate host in the form of one of the bivalve molluscs upon 

 which the final hosts feed. The larvse of one species, at least,. 



