CELETOZONE. 263 



3. Heterocirrus caput-esocis, De St Joseph, 1894. Plate CXI, fig. 10 — hook. 



Specific Characters. — Head forming a blunt cone like that of a pike, with two large 

 eyes placed over the posterior ganglionic region. Nuchal organs occur at the sides 

 behind the eyes. Proboscis short and bilobed. 



The body is larger than in the previous form, measuring 15 to 17 mm., and having 

 about eighty-four segments (De St. Joseph). Posteriorly it terminates in a conical tip, 

 the anal segment having at its base five festoons ventrally (De St. Joseph). In the 

 fragmentary example it tapered much anteriorly. The buccal and the next segment are 

 achaDtous, the latter giving rise to the large tentacles, with a branchia beneath each. 

 Bristles commence in the dorsal division on the third segment, and continue nearly to the 

 tail. Beneath the dorsal bristle-tuft is a pair of slender, long branchiae. The dorsal 

 bristles are joined in the last twenty-three segments by several of the peculiar hooks 

 (acicular bristles, De St. Joseph). The first ten or twelve bristled segments have capillary 

 bristles in both divisions ; thereafter the modified hooks take their place in the ventral 

 division. Hooks /-shaped with a curved distal region, which has a slight hook at the tip. 



Synonyms. 



1894. Heterocirrus caput-esocis, De St. Joseph. Ann. Sc. naf-., 7 e ser., t. xvii, p. 53, pi. iii ; figs. 58 — 60. 

 1898. „ „ Caullery and Mesnil. Annales Univ. Lyon, fasc. xxxix, p. 122. 



Habitat. — In small pools in limestone rocks at Babbacombe (Elwes). 1 



The head forms a rounded cone like that of a pike in life (De St. Joseph), and has 

 two conspicuous eyes, and behind them laterally the nuchal organs. 



The body ranges from 15 to 17 mm. or more in length, is more or less tapered 

 anteriorly, and still more so posteriorly, where it ends in a conical tip, the anal segment 

 having five " festoons " at its base ventrally. The anterior bristles are less conspicuous 

 than in H. viridis, but they occur in both divisions in the anterior ten or twelve 

 segments. Thereafter the dorsal bristles continue to the end, being joined in the last 

 twenty-three segments by one to four acicular bristles smaller than those in the ventral 

 division. The ventral acicular bristles or hooks (Plate CXI, fig. 10) quite differ from 

 those of any allied species, being /-shaped, with a hook at the distal extremity. 



De St. Joseph found ripe males and females, the latter with greyish eggs 0*12 mm. 

 in diameter. They occurred between the fourteenth anterior segment and the eighteenth 

 from the tip of the tail, and the ripe forms developed long bristles. He describes a pair 

 of large segmental organs in the first five bristled segments, opening externally on the 

 ventral surface of the first setigerous segment. Of the two ciliated internal branches one 

 is uncoloured, with a ciliated funnel in the second setigerous segment, and the other, 

 coloured brown, communicates with the external pore. 



Genus CIX. — Ch^tozone, 2 Malmgren, 1867. 



Head without appendages. A pair of large tentacles springing from the dorsum of 

 the next (buccal) segment, and accompanied by a branchia on each side. A considerable 



1 I am indebted to the courtesy of Major Elwes also for this example. 



2 Y/u'rrj ri et Zwvr) r\. 



