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Rh 40. Alope palpalis (White).—May be found in shady nooks amongst the rocks at low tide, but is not at all common. It must also occasionally swim freely, as I have taken it from the stomach of the "Jew-fish" (Sciæna antarctica). Covered with short red setæ. Palpi very large. Port Jackson.

41. Squilla lævis (Hess).—The common "Hass-crab" of Port Jackson. Caught principally in the Prawn-nets, travelling in company with Penæus esculentus, on which it partly subsists. It may often be procured from the stomach of Sciæna antarctica, of which fish it forms one of the principal articles of food. Coast of New South Wales.

42. Ceratothoa trigonocephala (Leach).—This is the commonest and best known of our fish parasites. As a rule, it inhabits the mouth of the "Yellow-tail," Trachurus declivis (C. & V.). The head is almost triangular, and deeply encased in the anterior portion of thorax. The Ceratothoa embryo is very different to the adult. The five segments of the pleon, which in the adult have coalesced, are movable upon each other. Pleon is nearly as long as pereion, but in the adult it is so insignificant as to be scarcely so long as one pereion somite. The telson too widens out posteriorly when the animal reaches maturity. Altogether the young Ceratothoa is fitted for a free existence, and no doubt the adult was the same at one time, but has been gradually adapted to living a parasitic life, thereby undergoing change of formation. Colour white. Port Jackson.

43. Nerocila sp.?—This Isopod is another of the parasitic Crustacea, having for its host the Sea-mullet, Mugil grandis (Cast.). It is not so convex as the preceding species, and the epimera are very long. Eyes are entirely wanting. Colour sometimes dark brown, also yellow.

44. Cymodocea pubescens (Hasw.).—The small crustaceans of this name are "rock-borers." The boring is done exclusively with the uropods, which form two strong spikes. In burrowing