Introduction. 5 



together with the Lophogastridfe, and appear to have been still undergoing development 

 in Carboniferous time. Indeed, it is highly probable that some member of the family 

 gave rise to the Squillid stock during, or soon after, the Carboniferous period, after 

 which they became extinct. 



The Anaspida3 are also regarded as having Ijranched off from the common 

 Mysid stem along with the two former families, and to have retained more primitive 

 characters than the others. They also seem to have reached their maximum 

 development during late Palaeozoic time. One branch of them, by retaining their 

 larval eyes, prol)ably gave rise to the modern Isopods and Amphipods by a very easy 

 transmutation, and seem to have been ousted bj^ their more advanced descendants, their 

 sole known survivor having taken to a fresh-water habitat in Tasmania, a country 

 that has long been isolated and rendered comparatively free from severe competition. 



The Mysidaj appear to have been even more highly specialised in Carboniferous 

 than in modern times. The structure of the existing members of the family seems to 

 have been simplified chieHy through degeneration. 



The Euphausiida2 seem to have been evolved from a Nebalid stock and to have 

 reached their full development in Carboniferous time, taking the place then that is 

 now occupied by our prawns and shrimps. The survivors have migrated to the open 

 sea, where the struoyle for existence is not so severe as alono- the shore. It is from the 

 Euphausiid stock that the Decapods have evidently arisen, and the evidence supplied 

 by the Scottish Carboniferous Eocks seems to favour the opinion that the branching 

 off had not even begun in the Carboniferous period. 



The following Table shows the genera and species grouped under the various 

 families already enumerated. Of the 34 species of fossil Schizopods, no fewer than 29 

 are represented in the Collection of the Geological Survey, while, of the remaining five 

 species, three are represented in the Natural Histor}' Collection of the Royal Scottish 

 Museum, Edinburgh : — 



[SCHE.ME. 



