ISOCIRRUS DA. 311 



also present. The keel, nuchal grooves, and frontal process are similar. No example is 

 perfect, but accompanying the anterior region is a detached funnel and adjoining unarmed 

 segments (four) which apparently pertain to a form of similar size, having twenty- 

 seven equal, or nearly equal, short conical cirri. The funnel is much softened, and no 

 anal cone is visible. In another fragment of the posterior end of a smaller example a 

 funnel occurs with a nearly similar number of cirri of like shape. An anal cone, slightly 

 pentagonal in form and somewhat eccentric in position, is present in this case. In a 

 funnel from the Skerries, Shetland, of similar size to the last, only twenty-three cirri 

 occur, and the anal cone is slightly marked. A feature in all the examples is the massive 

 condition of the ring at the base of the caudal funnel, for it forms a firm projecting shelf, 

 from the centre of which the base of the funnel arises. The cirri, moreover, stand 

 stiffly out. 



The body is typical in form, the first eight bristled segments anteriorly being 

 furnished abundantly with glands in belts, and the fourth segment has a collar anteriorly. 

 The first three segments are provided with spines, each of which shows a curvature of the 

 shaft, and the tip (Plate CJX, fig. 8) is rather acute, especially in the third set. In the 

 fourth segment is a characteristic row of hooks, which differ from the typical chiefly in 

 the greater length of the shaft, the diminished breadth of the neck distally, and in the 

 rudimentary condition of the gular bristles. The main fang also makes a larger angle 

 with the neck. The typical hook (Plate CIX, fig. 6a) has a somewhat short, curved shaft, 

 a well-marked elliptical shoulder, which gradually enlarges from below and diminishes 

 above — toward the neck; the latter then gently enlarges into the broad distal region with 

 the moderately high crown. The feature most distinctive, however, is the semicircular 

 notch below the great fang and its termination inferiorly in an eminence from which the 

 gular bristles spring, then slope obliquely upward to the tip of the fang, and curve above it. 

 The sharp main fang has a marked distal curvature, and stands nearly at a right angle 

 to the neck. At least six teeth occur in lateral view on the moderately elevated crown 

 behind the main fang, and the neck is boldly and obliquely striated, whilst the somewhat 

 slender shaft is longitudinally striated. The stronger bristles have nearly straight shafts 

 with tapered and often curved tips and distinct wings. The slender forms have spinous 

 tips and smooth shafts. 



2. Isocirrus DA, Mcintosh, Plate XCIX, figs. 4 and 4 a— anal disc : Plate 0, figs. 14 

 and 14a— head; Plate CIX, fig. 9 — hook; Plate CX, figs. 1 and 1 a— bristle and 

 hook. 



Synonym. 



1913. Isocirrus DA, Mcintosh. Ann. Nat. Hist., ser. 8, vol. xi, p. 95. 



Habitat.— Montrose Bay, April, 1869 (Dr. Howden) ; off Cape Guardia, 'Porcupine' 

 Expedition, 1870. 



Another form of Isocirrus (DA) of which only fragments of the posterior end with 

 the funnel came from Montrose Bay in April, and, along with Praxellella praetermissa, off 

 Cape Guardia in the ' Porcupine ' Expedition of 1870. Both belong to large forms of 



