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Part III. — Eighteenth Annual Report 



(fig. 17). The mandibles somewhat resemble those of Lepeoplitheirus 

 pectoralis. The sternal fork, which appears to vary to some extent, has 

 moderately stout bran ches; these branches are somewhat dilated in the middle 

 and slightly divergent (fig. 18). The branches of the fourth pair of thoracic 

 feet appear to be only two- jointed, like those of L. pectoralis ; each branch 

 is, for the most part, provided with five setae arranged as shown in the 

 drawing (fig. 19), but some specimens want the marginal seta on the end 

 joint ; the seta at the outer distal angle of the first joint is a very small 

 one. The fifth pair are broadly foliaceous, and situated beneath and 

 slightly anterior to the basal part of the ovisacs. 

 No males have been observed. 



Habitat — On the gills, inside gill-covers, and under the pectoral fins of 

 brill, Bothus rhombus, captured in the Firth of Forth and the Firth of 

 Clyde. 



It is very doubtful if the copepod described here, or the one described 

 under the same name by Dr. Basset-Smith, be the Lepeojphtheirus obscurus 

 of Dr. Baird's monograph. The copepod described by Dr. Baird as 

 Lepeoplifheirus obscurus was a male, and was probably, as he himself 

 suggests,* a male of Lepeoplitheirus liippoglossi . Figure 39, Plate V., of 

 the present paper represents an adult male of Lepeoplitheirus hipipoglossi, 

 and if Dr. Baird's figure of L. obscurus be compared ' with it the 

 resemblance between them will be seen to be very close. Moreover, Dr. 

 Baird, in describing Lepeophtlieiru* obscurus, says : — " Abdomen small ; 

 not more than one-third the size of last ring of thorax. . . . Sternal 

 fork well developed, each branch being bifurcated, the inner branch being 

 much smaller than the other." All this, as well as the remaining parts 

 of the description, agrees exactly with what we see in the male of 

 Lepeop)htli etrus hip} togloss i . 



The Lepeoplitheirus from the brill, described in the preceding notes, 

 resembles L. tliompsoni to some extent, and may probably be only a form 

 of that species. It seems to differ, however, in having a somewhat longer 

 abdomen ; in having the abdomen more distinctly segmented ; in the 

 sternal fork being rather different in form; and in the form of the fifth 

 thoracic feet being slightly different. 



Dr. Basset-Smith describes the sternal fork of his Lepeoplitheirus 

 obscurus as having bifurcating branches,f but in some other respects as 

 closely resembling L. tliompsoni. If the bifurcate form of the sternal fork 

 be a character more or less constant in Dr. Basset-Smith's specimens, they 

 are likely to be different from that which I have recorded, and that not- 

 withstanding their otherwise close similarity to Lepeoplitheirus tliompsoni, 

 for, as already pointed out, though the form of the sternal fork in my 

 specimen varies to some extent, in none of those examined has it been 

 observed to have bifurcated branches. 



The male specimen described by Dr. Baird as Lepeoplitheirus obscurus 

 may, in view of what has been stated by Dr. Basset-Smith, be after all a 

 distinct species, the female of which is the form recorded by that author, 

 and, if that be so, we have here another example of the want of uniformity 

 between the sexes of the same species, which is sometimes observed 

 amongst the parasitic Copepoda. This disparity between the sexes, how- 

 ever, is, I think, of less frequent occurrence amongst Caligus or 

 Lepeoplitheirus than it is amongst some of the other groups. If, for 

 example, the female Caligus or Lepeopjhtheirus be distinguished by a 

 short or a long abdomen, the male of the same species to which the 

 female belongs has usually, though perhaps not in every case, the abdomen 



* Brit. Entom., p. 363. 



f Journ. M. B. Assoc., Plymouth (April 1899), p. 158. 



