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
