It is in the Carboniferous epoch, in all probability, that we must look for the origin of most of the existing orders of Malacostraca. In the rocks of this age in different parts of the world there have been found a number of undoubted Malacostraca, nearly all of the shrimp-like form which there is good reason to believe to be a primitive characteristic. Some of these (_Pygocephalus_--Fig. 83) have recently been shown to possess a brood-pouch formed of overlapping plates on the under-side of the thorax, and thus resemble the existing Mysidacea, which stand at the base of the Peracaridan series of orders. Others have a pair of strong side-spines near the tip of the telson, and in other ways resemble the recent Euphausiacea, so that they may have been primitive members of the Eucaridan series. [Illustration: FIG. 83--_Pygocephalus cooperi_, FROM THE COAL-MEASURES: UNDER-SIDE OF A FEMALE SPECIMEN, SHOWING THE OVERLAPPING PLATES OF THE BROOD-POUCH. (From Lankester's "Treatise on Zoology," after H. Woodward.)] [Illustration: FIG. 84--THE TASMANIAN "MOUNTAIN SHRIMP" (_Anaspides tasmaniæ_), A LIVING REPRESENTATIVE OF THE SYNCARIDA. SLIGHTLY ENLARGED _c.gr._, "Cervical groove," marking off the first thoracic somite; ii-viii, the remaining thoracic somites; 1-6, the abdominal somites] Among the Crustacea of the Carboniferous and Permian epochs, there are a number of forms of which the affinities were until recently quite obscure. They have two-branched antennules, a scale-like exopodite on the antenna, and the last pair of appendages (uropods) form, with the telson, a tail-fan. In these points they resemble the shrimp-like forms, but there is no carapace, and all the somites of the thorax are distinct, so that the form of the body is rather that of an Amphipod or Isopod. On the discovery of the remarkable Crustacean _Anaspides_ (Fig. 84), which lives in fresh-water pools in the mountains of Tasmania, it was pointed out that it agreed with the fossil genera _Uronectes_, _Palæocaris_, and their allies, in those very characters in which they differed from all other Crustacea, and that it must be regarded as a surviving representative of the ancient group to which the name of Syncarida had been given. The more recent discoveries of living forms, _Paranaspides_ from the Great Lake of Tasmania and _Koonunga_ from fresh-water pools near Melbourne, and of the fossil _Præanaspides_ (Fig. 85) from the Coal-measures of Derbyshire, have tended to support this conclusion. There can be little doubt that the Syncarida arose during the Carboniferous epoch (or earlier) from primitive shrimp-like forms which lost the carapace; but, after flourishing for a relatively brief period, the group dwindled away, although a few survivors have lingered on, like so many other "living fossils," in the isolated Australian region.