Gatty Murine Laloratory, St. Andrews. 1*5 



and the fourth segment has a collar anteriorly. The first 

 three segments are provided with spines, which show a 

 curvature of the shaft, and the tip is rather acute, especially in 

 the third set. In the fourth segment is a characteristic row 

 of liooks, which differ from the typical chietly in the greater 

 length of the shaft, the diminished hrcadth of the neck 

 distally, and in the rudimentary condition of the gular 

 bristle's. The great fang also makes a larger angle with the 

 neck. The typical hook 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 dilates 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 great 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 very finely 

 tapered hair-like tips. 



Another form of Isocirrus (DA), of which only fragments 

 of the posterior end with the funnel come from Montrose 

 Bay, April 1869 {Dr. Hoivden) ; and along with Pra.villella 

 praterniissa, off Cape Guardia, in the ' Porcupine ' Expedition 

 of 1870. Both belong to large forms of about the same size. 

 Both have an elevated ventral streak which passes to the 

 edge of the funnel, and both have short, stiff, conical cirri, 

 which in that from ^Montrose Bay are thirty in number, 

 whilst in the more beautiful specimen from the ' Porcupine ' 

 there are thirty-seven more acutely conical cirri. A slight 

 anal cone is also present in the latter, but this is due to 

 difference in contraction in life. Minute processes surround 

 the anal aperture. The firm rim or shelf from which the 

 caudal funnel arises is the same in both, and it has in front 

 of it two unarmed segments with lateral glandular areas. 



The hooks are comparatively large in the posterior region, 

 the shafts are but slightly bent, the shoulder moderately 

 developed, and the neck long. Moreover, the form of the 

 neck is diagnostic, since the prominence from which the 



