This little shrimp (Fig. 78), which does not appear to grow to more than an inch in length, is totally different in appearance from _Anaspides_, being pale green and transparent, with a very marked dorsal hump as in _Mysis_, to which it bears a very striking superficial resemblance. It leads a more active swimming life than _Anaspides_, and with this habit is correlated the flexure of the body and the greater size of the tail-fan and the scale of the second antenna. The mandible is peculiar in being furnished with a four-jointed biramous palp, while that of _Anaspides_ is three-jointed and uniramous, and the first thoracic appendage is provided with a setose biting lobe on the antepenultimate joint, thus more resembling a maxillipede. In other respects it agrees essentially in structure with _Anaspides_. [Illustration: FIG. 78.—_Paranaspides lacustris_, × 4. _a^1_, _a^2_, First and second antennae; _Ab.1_, first abdominal segment; _ep_, epipodites or gills on the thoracic legs; _md_, mandible; _Pl.1_, first pleopod; _T_, telson; _Th.8_, eighth free thoracic segment; _U_, uropod, or sixth pleopod. ] =Fam. 2. Koonungidae.=—The sole representative of this family, _Koonunga cursor_, has been recently described by Mr. O. A. Sayce,[94] of Melbourne University, from a small stream some miles to the west of Melbourne. Although plainly belonging to the Anaspidacea, this interesting little animal, which only measures a few millimetres in length, and follows a similar habit to _Anaspides_, running about with its body unflexed, differs from all the other members of the Division in possessing sessile instead of stalked eyes, in the first thoracic segment being fixed to the head, and in a number of minor anatomical points. It is impossible at present to assign the Carboniferous forms (_Gampsonyx_, _Palaeocaris_, etc.) to their exact position in the Division, but it seems that they agreed more closely with _Anaspides_ than with the other two genera. From the position in which the fossils are preserved, it would appear that they followed a similar walking habit to _Anaspides_, and that the body was unflexed. DIVISION 2. PERACARIDA. The carapace, when present, leaves at least four of the thoracic somites distinct; the first thoracic segment is always fused with the head. The eyes are pedunculate or sessile. The mandible possesses a lacinia mobilis. A brood-pouch is formed in the female from oostegites attached to the thoracic limbs. The hepatic caeca are few and simple; the heart is elongated and tubular; the spermatozoa are filiform, and development takes place without a complicated metamorphosis. =Order I. Mysidacea.=