CAPITELLIDJS. 269 



No special differentiation separates the first region of the body from that which 

 follows, and therein it differs from the ChaBtopterids ; bnt the first segment of the 

 succeeding region is three times broader (antero-posteriorly) than those in front, and its 

 bristles are shorter and structurally different, whilst each of the two divisions carries a 

 continuous row of stout, curved crotchets without the differentiation between shaft and tip 

 as observed in Chaetozone (Plate CVII, fig. 14 a — representing one from the tenth foot). 

 Dorsally are two smooth capillary bristles, followed by five or six crotchets with the tips 

 produced into slender processes, and then a series of the stout, curved crotchets with 

 slightly tapered tips ending in a stout, though more or less pointed, tip. The arrangement 

 of these crotchets recalls the condition in Chaetozone setosa, bristles being also interposed 

 between the crotchets in the rows. 1 



Famtly XXTTT. — CJAPiTKriTiTPiB, Oruhe ; Halelminthld^e, Mahngrea ; Halelmlnthea, V. Oarus. 



The cephalic region is pointed, and has two relatively small balaniform (nut-shaped) 

 retractile tentacles. Eyes in the form of pigment-specks. The peristomial segment is devoid 

 of bristles. An eversible, papillose, and boring proboscis issues from the ventral mouth. 

 Body long, reddish, rounded, with distinct segments, and of two regions— the first of nine 

 to fourteen segments and a cuticular mosaic, with rudimentary feet and capillary bristles ; 

 the second with slightly retracted rows of hooks, and terminating posteriorly in an anus 

 with papillas. Branchise at the ends of the rows of hooks in the posterior part of the body, 

 conspicuous or partially or wholly retractile, and containing hsemolymph (ccelomic fluid), 

 the corpuscles being coloured, the plasma colourless. Sense-organs and ciliated organs 

 present. In most of the segments side-organs in a groove on the anterior region, free on 

 the posterior region. Cup-like organs on the proboscis, head, and body. Cephalic ganglia 

 and oesophageal ring in the head and first two body-segments, followed by nerve-cords which 

 lie free on the body-cavity, the oblique muscles descending beneath. The only circulatory 

 system is the hsemolymph in the ccelom. Segmental organs in most segments, or 

 confined to a region. 



Sexes separate. Reproductive organs consist of genital pouches and copulatory 

 organs in the male, with vesiculse seminales and penes with strong hooks ; in the female, 

 ovary, receptacula seminis, and vulvas. Larva free with metamorphosis. They live in 

 sand and mud into which they bore. 



In Notomastus latericeus the type of the body-wall differs much from that of the 

 Cirratulidse, and, besides, the longitudinal muscles are asymmetrical, for a median muscle 

 of great power occurs in the mid-ventral line (Fig. 128), and thus the nerve-cords are 

 borne inward to its upper surface. Externally are the cuticle and moderately developed 

 1 Whilst this sheet is passing through the press Mr. Southern has considerably added to our 

 knowledge of the Cirratulidge of the west coast of Ireland. Thus he describes Cirratulus Mclntoshi 

 (= C. norvegicus, Mcintosh), Choetozone alata, n.s., G. Killariensis, n.s., and Macrochxta clavicomis, 

 Sars. ' Proc. Roy. Irish Acad./ vol. xxxi, no. 47, pp. 110—120, pis. xii and xiii. These and other 

 additions to the Polychset Fauna will subsequently be noticed. 



