A HISTORY OF DERBYSHIRE 



the Amphipoda agree more closely with the crabs and lobsters, which 

 have the breathing apparatus in the same situation, although their 

 breathing organs are out of sight under the sides of the carapace and 

 are far less simple in structure than those of the sessile-eyed group. 

 The species Gammarus pulex (Linn.), occurs in Derbyshire, as it occurs 

 all over England where there are pools and rivulets. At Matlock Bridge 

 I took it in wet moss from a trickling stream not half an inch deep, 

 and likewise from a little pool which at the time was only an inch or 

 two in depth. Specimens have also been sent me by Dr. H. Lyster 

 Jameson, M.A., from water in Speedwell Mine. That other amphipods 

 will be found in Derbyshire when its wells and cavern waters are searched 

 for the purpose is highly probable. 



Of Entomostraca in this district there is little at present to be said. 

 Only one of the great sub-divisions appears to have been hitherto in any 

 way noticed. This one is the vast group of very small and very active 

 animals known as the Ostracoda. They belie their affinity to shrimps 

 by assuming the appearance of tiny mussels. In spite of the enclosing 

 valves many of them swim with remarkable agility and thus present a 

 strong contrast to the sedentary habit of the true mussels among the 

 Mollusca. But some of the species are content to creep, a change of 

 manners and morals to which testimony is borne by the generic name 

 Erpetocypris. The word is intended to mark a stage of evolution. 

 From the lively genus Cypris, it is supposed, certain forms have descended 

 so modified for a lethargic mud-loving life that the prominent attribute 

 of their race has been lost, and the creature is consequently stigmatized 

 as ' the creeping cypris.' Of the genus so named this county possesses 

 two recorded species, Erpetocypris tumefacta (Brady and Robertson), which 

 has been ' taken in the river Lathkill, Derbyshire,' and E. o/ivacea, Brady 

 and Norman, of which the authors say : ' This pretty species was found 

 abundantly amongst weeds in the river Lathkill.' Both by shape and 

 colouring they are well distinguished. The former has the ' shell per- 

 fectly smooth, opaque white or cream coloured, with clouded yellow 

 patches, and sparingly coated with very fine hairs.' ' Of the latter the 

 shell is ' smooth and shining, transparent, mottled, deep olive green.' a 

 Of E. tumefacta Brady and Robertson remark that a side view might 

 lead to a confusion of it with Cypris sirens or Cypris incongruens, but that 

 ' no species possesses a more characteristic or well-marked contour when 

 looked upon from above,' and in this respect they describe it as ' broadly 

 ovate, suddenly and acutely mucronate in front, well rounded behind, 

 sides sub-parallel, greatest width situated in the middle, and somewhat 

 greater that the height.' s On the other hand E. o/ivacea is, when ' seen 

 from above, ovate, more than twice as long as broad, widest in the 

 middle, extremities obtusely pointed and nearly equal,' so that the ex- 

 tremities from this point of view are sufficiently distinctive. The only 

 other Ostracode definitely named as occurring in the county is Cypridopsis 



1 Brady and Norman, Trans. R. Dublin Sue. (1889), ser. 4, iv. 87. 2 Loc. cit. p. 89. 



8 Annak Nat. Hist. (1870), ser. 4, vi. 13. 



1 08 



