CRUSTACEA FROM EAST COAST OF SCOTLAND 153 



the " Tenth Annual Report of the Fishery Board for 

 Scotland" (1892). 



Lichomolgus arenicolus appears to be a rare species. 

 Some important details of structure not noticed in " British 

 Copepoda " are here described and figured, as are also 

 several others, to illustrate the description of the species, 

 viz. : the posterior antennae with its remarkably articulated 

 and clawed terminal spines, the rudimentary female pos- 

 terior foot-jaw, and the fourth pair of swimming-feet, which, 

 like the other three pairs, has both branches three-jointed, 

 and which in this respect forms, with Lichomolgus aberdon- 

 cnsis, Lichomolgus littoralis, and Liclwmologiis sabellce} a 

 distinct group — the other species of Lichomolgus being 

 distinguished from these three by having the inner 

 branches of the fourth pair of swimming - feet one- or 

 two-jointed. The one- or two-jointed inner branches of 

 the fourth pair of feet constitute one of the characters 

 of the genus Lichomolgus, while a second character is that 

 of the mandible, which has the form of " a slender stylet, 

 dilated at the base, but excessively slender and filiform 

 beyond the middle." In Lichomolgus arenicolus there are 

 two mandibular stylets, and in Lichomolgus aberdonensis and 

 littoralis the mandible, which is moderately stout and broad, 

 has no stylets, but is armed at the extremity with one or 

 two tooth-like processes and a few set;e. In consequence of 

 this divergence from some of the generic characters of 

 Lichomolgus, it may become necessary to institute one, or 

 possibly two, sub-genera for the reception of these aberrant 

 forms, or otherwise to alter the generic definition of 

 Lichomolgus so as to include them. 



Should it be found desirable, for the reasons stated, to 

 remove Lichomolgus littoralis and aberdonensis into a different 

 genus or sub-genus, we would suggest Platycheiron as an 

 appropriate generic name, — being descriptive of the remark- 

 ably broad ultimate joint of the male posterior foot-jaws 

 of the two species referred to. 



1 A species described by I. C. Thompson in '• Proa Liverpool Biol. Soc.,"vol. 



ii. p. 68. He also records /.. aibens t Thorell, from Liverpool Bay, but we have not 

 as yet seen any description of tliis species. Another species (apparently new . 

 having the inner branches of the firsl four pairs of swimming-feet three-jointed, 

 has just been obtained by us, anil will be described and figured later. 



