438 MESSES. T. AND A. SCOTT — BE VISION OF THE BRITISH COPEPODA 



Description. Length '55 mm. (^^5- of an inch). Body very slender; the forehead, 

 seen from the side, is small and sharply rounded to form the small beak-like rostrum 

 <P1. 36. fig. 17). 



Antennules 6-jointed, elongate, slender, and sparingly setiferoiis ; the third joint is 

 considerably longer than any of the others, but the last joint is vex-y small, as showTi by 

 the formula : — 



No. of the joints : 1.2.3.4.5.6 



Proportional lengths : 10 8 18 11 11 3" 



Antennae slender ; secondary branches ;3-jointed, longer than the second joint of the 

 primary branches ; the first two joints are small, the other is elongate (PI. 37. fig. 6). 

 Basal jomt of the mandibular palj) comparatively small and furnished with a stout sub- 

 marginal plumose seta ; the superior apical branch is nearly as large as the joint to 

 which it is articulated, and is armed with a stout spiniform and semiplumose seta and 

 also with several plain setae ; the inferior marginal branch is extremely small (PL 37. 

 fig. 23). The anterior foot-jaws closely resemble those of Ectluosoma Sarsi, but are 

 much smaller (PI. 37. fig. 35). Posterior foot-jaws short, moderately stout, somewhat 

 cylindrical in form, and with the terminal joint very short (PI. 37. fig. 50). 



First four pairs of swimming-feet slender. In the first pair the outer branches are 

 scarcely equal in length to the inner branches, but in the fourth pair both branches are 

 of about eqtxal length (PI. 38. figs. 11 and 16). 



Fifth pair small ; the produced inner portion of the basal joint extends to about the 

 apex of the secondary joint ; two slender and very long plain sette spring from the apex 

 of the secondary joint, and one from the produced inner portion of the basal joint ; both 

 joints are also furnished with a small seta at the inner distal angle, in addition to a 

 transverse row of small spines, as shown in the figure ; a slender seta also springs from 

 the lateral aspect of the secondary joint (PL 38. fig. 38). 



Caudal stylets short (PL 38. fig. 53). 



Abdomen clothed with indistinct transverse rows of minute hairs ; the posterior 

 margins of the segments of the thorax and abdomen are also fringed as in most of the 

 other species described here. 



Habitat. From various parts of the British coasts, both inshore and in the open sea, 

 and in dredged material, as well as in toAV-net gatherings — as, for examj)le, in the 

 Atlantic, off the west coast of Ireland and in Kinsale Harbour ; in various parts of Loch 

 Fyne ; in various parts of the Firth of Forth (we have taken Ectinosoma atlanticum 

 both with the dredge and with the tow-net in the Firth of Forth, and it was very 

 common in material collected in a large flannel sieve used for filtering the sea-water 

 that is pumjoed into the fishpond at the Dunbar hatchery). 



'Remarks. After a careful study of numerous specimens of Ectlnosoma atlanticum, 

 we, like Dr. G. S. Brady *, can find no valid reason for separating this species from 

 Ectinosoma. It no doubt differs from the typical Ectinosoma in the greatly disjiropor- 

 tionate sizes of the branches of the mandibular palp and in the structure of the posterior 



* ' Monograph of the British Copepoda,' vol. ii. p. 14 (ISSO). 



