122 MB. G. S. BEADY ON THE CEUSTACEAN FAUNA OF THE 



Crangon vulgaris, My sis vulgaris, Oammarus locusta, Corophium 

 longicorne, and Spliaroma rugicauda : in Hylton Dene I met also 

 with. Orchestia littorea, and at Seaton Sluice with Oniscus asellus. 

 These usually occur in considerable numbers, though very often 

 a pool will be found tenanted entirely by one species to the ex- 

 clusion of the rest, while a neighbouring pool will contain a mix- 

 ture, or perhaps a single different species. In Hartlepool Slake 

 I have seen the water so swarming with Mysis vulgaris that a 

 net could not have been dipped in the spaces between the float- 

 ing balks of timber without captui'ing scores or perhaps hundreds 

 of them. 



The Entomostracan inhabitants of salt-marshes seem to be 

 confined to the two orders, Ostracoda and Copepoda. In pools 

 which are subject to the overflow of ordinary spring-tides the 

 Ostracoda met with are Cythere castanea, Cytlieridea littoralis, and 

 Loxoconcha elliptica, the last named until recently an unde- 

 scribed, and apparently a rather uncommon species ; the other 

 two are of very frequent occurrence, C. littoralis often existing in 

 astonishing abundance. But in the sub-brackish pools slightly 

 above tidal influence, which have been already referred to, we 

 find two Cypridae which seem to have a pai'ticular liking for 

 these situations, though both are occasionally found in quite fresh 

 water ; these are Cyp>ris salina and Cypridopsis aculeata. The 

 only locality in which I have found the two species in company 

 is a hot-water pond at Monkwearmouth Colliery, the water of 

 which, though of course not at all marine in character, is, never- 

 theless, owing to its rapid evaporation, constantly saturated with 

 salts of lime, &c., which it deposits copiously in a sort of crust 

 upon the vegetation (Potamogeton, Callitriclie, &c.) which it con- 

 tains. Besides this locality C. salina has been found only twice 

 by Dr. Baird and myself, and in both cases in pools just above 

 high water. The Monkwearmouth pond seems also to afi'ord the 

 only instance of the occurrence of C. aculeata apart from salt 

 water, unless, indeed, one of the Sufl"olk "broads," where it was 

 taken by Mr. E. C. Davison, be an instance of fresh-water habi- 

 tat. I believe, however, that even this may probably be rightly 

 called a sub-brackish habitat. 



