XEPHTHYS LONGISETOSA. 31 



shaped tip of ruptured radiate muscular bands which are fixed to the next region. On 

 each side a strong series of fibres forms a triangular muscular sheet, narrow posteriorly, 

 which is inserted into the hollow of the constriction about a third from the front. 

 Thereafter the organ gently dilates, again to contract posteriorly where it joins the gut. 

 A slight ridge, commencing behind the pit at the muscular belt, marks the dorsal median 

 line, and a slight furrow the corresponding part of the ventral surface. This region has 

 fine transverse lines as in the proboscis of the Aphroditidse. 



When the organ is completely retracted, the protractor muscles form long bands 

 (Plate LVII, fig. 12) from the snout backward to the dense proboscis, the special triangular 

 bands at each side, again, acting on the latter in eversion, so as to tilt it outward. 



The typical foot is not much produced, and shows dorsally an elevated and conspicuous 

 lamella of a semicircular or truncated broad ovoid form (Plate LXVI, fig. 11) with a 

 continuation appearing as a small rounded process or flap while the interfascicular lobe 

 slants from above downward and outward with a prominent papilla for the spine, after 

 which the margin recedes. A small free flap occurs at the outer margin of the fillet 

 guarding the base of the barred bristles. The base of the branchia is closely connected 

 with the dorsal cirrus, only a shallow notch separating them. The cirrus is lanceolate, 

 broad and flattened at the base, pointed at the tip. It is interesting that the same 

 structure in A T . trissophythus, Grube, from Naples, is largely developed into a thin lamella 

 like the cordate leaf of the lime. The branchia is often coiled inward. The barred 

 bristles offer no diagnostic feature except their strength (Plate LXXVII, fig. 8a). The 

 long serrated bristles are remarkably strong, with a pale yellow metallic sheen, and 

 curve backward. The flattened blade gently bends from the shaft, its convex edge being 

 minutely serrated with rows of spikes (Plate LXXVII, fig. 8 and 8b). 



The inferior division presents two flaps superiorly, the upper edge of the bristle-fan 

 passing between them. The anterior lamella is the larger, is tongue-shaped, and has a 

 further modification of the small process observed in other forms, e.g., K ciliata, 0. F. M. 

 The lower angle of the same fillet often has a small free flap. The spinigerous region forms 

 an acute triangle with the spine at the apex. The inferior lamella is comparatively small 

 and somewhat resembles an ovate leaf, but there are considerable differences in regard to 

 the development of this lamella, the Zetlandic form especially having it well-marked with 

 the tip pointing upward and outward. The ventral cirrus is large and lanceolate with a 

 central rib, and an articulation at its base. Both barred and serrated bristles are largely 

 developed, the latter presenting a gentle curve from base to apex, the minute spines being 

 traceable from the short shaft to the tip. 



In contrast with K caeca, the inferior oar of the foot in N. longisetosa is less 

 prominent, and does not project so far outward. The bristles of the entire foot are also 

 much more strongly marked (not longer), and have a decided curve backward. In 

 K longisetosa those with the serrations at the side are broader at the dilated portions. 

 The inferior lobe is little developed, and thus strongly contrasts with several of its allies. 

 The inferior cirrus is lamellate, and broader than in most. The serrations on the edges of 

 the bristles are less conspicuous than usual; or they resemble the slated markings of 

 wool rather than sharp and independent serrations. This gives a character to the bristles. 

 The process at the base of the sickle-shaped cirrus is rather long and lanceolate. 



