132 M. W. Lllljeborg on two remarkable Crustacea the occipital to the angle of the raoiith (as in C. trhnaculatus) ; a black horseshoe-like collar^ with the convexity directed forward ; a black line runs from the collar to the tip of the tail, along the vertebral series of scales ; a series of roundish black spots, in-distinctly edged with white, along each side of the anterior part of the trunk. Tail coloured like the bodj'^, without black rings. Upper labials seven. Thirty inches long. Two specimens, from the Fort Pitt Col-lection, are in the British Museum. They are said to be from British India, locality unknown. P.S. — Elajjomorphus mexicaniis and Hydrophohus semifasciatus (PI. IX. figs. 1 & 6) are represented twice their natural size. Add to the first list Tretanorhinus variabilis, from Cuba, which has lately been received through the kindness of Prof. Peters. This raises the total number of species in the British Museum to 612, which are represented by more than 4100 spe-cimens. According to a statement of Prof. A. Dumeril (Arch. Mus. ix. 1857), the Paris Collection contains 523 species. XVI. — An Account of two remarkable Crustacea of the Order Cladocera. By W. Lilljeborg*. [Plate VIIL] The two Cladocera which I am about to describe are of so remarkable a structure, that I have not thought myself justified in delaying their description, as I had previously intended, until I had an opportunity of issuing a continuation of my treatise on the Cladocera, Ostracoda, and Copepoda. Both are found in our fresh waters, and are widely disseminated. Baron G. C. Ceder-strom, to whom, in this branch of knowledge, we are so greatly indebted, first drew my attention to the one species, and also transmitted to me specimens of the other. The former differs so widely from all Cladocera hitherto known as to form a separate family ; but the latter belongs to the Polyphcmidsc, although in some respects it strikingly deviates from the other members of that family. That the former has not previously been noticed may be ascribed to the circumstance that it is so transparent as to be seen only with difficulty, although it is larger than any other Cladocera, — on which account it may well be contained in a glass of water without being seen, even with the aid of a lens. The other seems to be very rai-e, and probably has its abode in deep water. * From 'Ofversigt af Kong. Vet. Akad. Forhandl.' Read May 16, 1860.
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