of the North A tlantic and of North- Western Europe. 655 



slightly arcuate, descending suddenly in front ; posterior margin rather obliquely 

 truncate, with an angle at the junction with the ventral margin ; anterior margm 

 highly vaulted, from the summit of the vault an oblique truncation descends to 

 form the rostrate process, which is very broad, and angled at the extremity ; it 

 overhangs the moderately deep sinus, which is distinctly inferior, and widely 

 open, and has its lower margin nearly straight, and uniting with the ventral 

 margin in an obtuse angle. Surface of valves everywhere pubescent, with 

 short erect hairs. Seen from above the form is elongo-ovate, the sides evenly 

 arched, the greatest breadth central, and equal to half the length. Length of 

 G-reenland specimens 3 mm., height 2 mm. Scandinavian and British specimens 

 slightly less. Colour pale yellow. The antennas in the ? have the tactile seta of 

 the small branch of considerable length, and the terminal spine hook-shaped, 

 curved, and forming a prehensile organ with the flattened joint from which it 

 springs. The masticatory process of the mandible is very deeply divided, and 

 the masticatory spines are furnished with a single stout lateral prong. Vibratory 

 lamina of the penultimate limbs narrowly triangular, and edged with about fifteen 

 setse. The vermiform last limb (PI. Li., figs. 2, 3) is furnished with more 

 numerous spines than usual, of which about sixteen are at the extremity, and 

 eleven on the sides; the distal portion of the spines is furnished with 7—8 

 serrations on each side. Ungues of the cauda about eighteen ; the two ultimate 

 pairs have strongly spined edges, the rest are not spined but ciliated; in the 

 male the spinose and ciliated garniture of the ungues is more delicate than in 

 the female. 



The male has the shell of very different form than that of the female ; the 

 outline is more oblong, the height about three-fifths of the length ; both ventral 

 and dorsal margins are only slightly arcuate ; the posterior extremity is rather 

 obliquely truncated, as in the female, but the inf ero-posteal corner is well rounded, 

 and devoid of the angularity of the other sex ; the anterior sinus is very shallow, 

 but widely open, the highly-vaulted anterior extremity rising perpendicularly 

 from the bottom of the sinus thence arches backwards, so that the overhanging 

 portion, characteristic of the female, is quite obsolete. The surface of the valves 

 has, in addition to the pilose investiture, longer setaj sparsely distributed over the 

 posterior portion. The grasping branch of the antenna of the male (PL li., fig. 1) 

 has the second joint slightly curved backwards, and furnished with three closely- 

 ringed flagella on the inner margin, the third joint is formed for reflection on the 

 second, and arcuate in a reverse way to the latter, on which it closes ; the inner 

 face smooth, furnished with one closely-ringed flagellum near the base, and a 

 minute seta at the tip. 



Hahitat. — Off the coast of Durham, near the Dogger Bank, 1862 (A. M. N.). 

 "Off Noss, in Shetland, 80-90 fathoms " (M'Audrew). 



4Z2 



