490 Dr. Johnston's Contributions to the British Fauna. 



two basal joints short and equal, the two following a little longer. 

 Thighs as long as the coxce, very slightly dilated. Tibiw of two 

 equal joints, each nearly as long as the thigh. Tarsi three-articu- 

 late, first minute, second rather long, falciform, with a few teeth 

 on their internal edge, and terminated by a single rather long 

 claw. Tail without any appendage. 



I have entered into this particular description, since there may 

 be some doubt of the correctness of referring the animal before us 

 to the genus Nymphum, I had it alive several days, during which 

 it was repeatedly examined, but could discover no trace, either 

 from its motions, or from careful inspection, of its having lost any 

 organ: yet there are no palpi^ nor egg-bearing organs. The 

 number of joints in the legs, and their proportional lengths do not 

 agree with those assigned to the genus by Dr. Leach ; from which 

 circumstance I may infer with some confidence that it is synony- 

 mous with neither of his species. When at rest with its legs 

 drawn up, it so closely resembles some of the fine coloured Con^ 

 fervce but more especially a detached portion of the Chondria 

 articulata, as to be easily overlooked. It appears to me interest- 

 ing in so far as its transparency allows us to examine its circulating 

 system with an accuracy which perhaps no dissection could enable 

 us to amend. Close to the tubercle we see the vessel (for there 

 is no heart) divide into two equal branches, one to each mandible; 

 and the flux and reflux of a fluid is easily observable in them, more 

 particularly in one, as in it there was a black particle which moved 

 alternately backwards and forwards with the motion of the fluid. 

 From the tubercle the vessel runs down the body, giving off a 

 single branch, equal in size to the trunk, to each leg ; and this 

 branch continues uninterrupted to the tarsus. Neither in the 

 trunk nor branches could we perceive any movement of the fluid. 



Gammarus punctatus. 



To my description of this species I wish to add that it dwells in 

 a furrow from one to two inches long, composed of pieces of sea- 

 weed, and lined internally with a thin, smooth and glutinous 



