1 76 THBLEPUS CINCINNATUS. 



shows no enlargement, and the tip is hair-like. No regular series of short bristles 

 occurs in these tufts, though one or two are observed at the edges. 



The first row of hooks is on the fifth segment, the first two elevations being devoid 

 of them. On the fifth the row is at the posterior part of the segment at some distance 

 ventrally from the setigerous process. They increase a little in length after the first 

 and remain nearly equal for a considerable distance, gradually, however, becoming 

 elevated, so that about the twenty-fifth, prominent uncinigerous processes are formed 

 and posteriorly they stand out like the " legs " of caterpillars. Toward the tip of the 

 tail they diminish on the narrow segments and incline ventrally, so that those of opposite 

 sides approach, and they cease at the last segment. In an example from St. Andrews 

 the uncinigerous processes were irregular posteriorly, being crowded on one side, and 

 scantily distributed, even with blanks, on the other — probably from injury. The hooks 

 are arranged in a single row throughout and are smaller than those of Lanice conchilega, 

 but more numerous, no less than 137 occurring in a row anteriorly, but posteriorly 

 the number diminishes. Each hook (Plate CXXVI, figs. 6 a— d) in lateral view 

 presents two teeth above the main fang. The posterior outline is short and has a dimple, 

 whilst the base is elongated and convex interiorly. The anterior outline (below the 

 main fang) is smooth, often slightly convex, and merges into the prow (anterior 

 part of the base), which is prolonged as a stout process with a slightly dilated tip, so 

 as to resemble a stud, whilst below this the prow curves a little forward, and the inferior 

 outline is slightly convex. In some a smaller process of the prow (less than that shown 

 in fig. 6 6) occurs beneath the stud, as, for instance, from the south-west of Ireland. 

 The occasional occurrence of a second tooth above the main fang brings the Heterophenacia 

 Renouardi of Marion, 1 from Marseilles, nearer this species. 



The tube is generally attached inside bivalves from deep water, and contains more 

 of the tough membranous secretion and fewer shelly elements than that of Lanice 

 conchilega; moreover, its anterior end is not branched. The anterior glands and the many 

 glandular bodies which give a variolous appearance generally may also aid in the secretion, 

 and in some the body is surrounded by a milky secretion before death. When in vigour 

 the animal rapidly constructs a tube. In many the tube shows a tendency to assume a 

 spiral form. The forms attached to the secretion are spines of Amphidoti, fragments 

 of shells, corallines, masses of mud and Foraminifera, ' In Greenland the tubes of 

 the arctic type are sometimes made of sand and Foraminifera (Ditlevsen). In the 

 Mediterranean they are formed of coralligenous algse, leaves of Posidonia, vegetable fibres 

 and other debris (Lo Bianco). 



Reproduction. — In an example captured on the 16th October numerous ova were 

 found in the coelomic space. Lo Bianco (1909) observes that individuals carried ova 

 from August to October at Naples. 



A distinct variety of Thelepus cincinnatus, if not a separate species, was dredged 

 by the "Knight Errant" at Station 8, lat. 68° 4', long. 7° 37', in 305 fathoms on mud. 

 Only the hook is at present available, but it differs from that of the ordinary form 

 in the depth and proportional shortness of the base, which is boldly convex inferiorly. 

 It agrees with the northern Thelepus in having only a single tooth above the main fang. 



1 ' Eevue des Sc. nat./ t. iv, March, 1876. 



