A HISTORY OF RUTLAND section Calyptomera. The family Daphniidae, in which our first three species are comprised, has, among others, these characteristics. The second antennae have one branch four-jointed, the other three-jointed, and the intestine has in front a pair of caecal appendages, but is devoid of median loop. On the other hand, the family Chydoridae, to which the four remaining species belong, has both branches of the antennae three-jointed, the intestine generally without anterior caecal appendages, but looped in the middle, and commonly having a simple caecal appendage at the rear. In the first family, ScaphoUheris mucronata (O. F. Miiller) is an attractive little species, about one millimetre or a twenty-fifth of an inch long, not easy to mistake when once known. The valves of the carapace, at the meeting of the hind with the straight setose ventral margin, are produced into acute processes, a conformation which makes it easy to set up a specimen for dorsal survey. Some of the Oakham specimens had the upturned frontal horn, on account of which a variety cornuta has been named, or even established as a distinct species. There were examples of this form containing the dark solitary ephippial egg, as figured by Lilljeborg.^ They were obtained between the 9th and the 1 2th of August. Discussing the varied habits of Entomostraca, Mr. D. J. Scourfield observes that — Some forms swim continuously in the open water of clear ponds and lakes, some attach them- selves in various ways to weeds, some crawl about the bottom, some burrow in the mud, some live habitually in wet mosses, and so on. But of all the peculiar modes of existence, that of deliberately making use of the ceiling of a pond, i.e. the surface-film of water, for support, is probably the most remarkable. So far as is known, only a very few species have acquired this power in a fully-developed fashion, and these are all included in two genera — namely, Scapho- leber'u (Cladocera) and h'otodromas (Ostracoda).' Taking the present species for an example, he explains that on the ventral margin of each valve the setae at either end of the series project somewhat more than the rest, and when the animal, which habitually swims on its back, brings this margin into contact with the surface of the water, the projecting setae pierce the surface-film, and produce minute capillary depressions, sufficiently large to support the difference in weight between the animal's body and the water which it displaces. He suggests that in this position it obtains some of its food from the miscellaneous organic particles which collect on the surface. Mr. Scourfield further ingeniously suggests that it is protected against the risks of its unusual position by the peculiar duskiness of its whole ventral surface, observing that, in consequence of this darkening, it ' is certainly much less noticeable when seen from above over a muddy bottom than it would otherwise be.' ' As Cladocera in general avoid the surface-film, the unusual position may in itself help to safeguard Scapholeberh against enemies from below. Simosa vetula (O. F. Miiller) is a much larger species than the preceding, and, its valves being deeper behind than in front, its lateral aspect is rather clumsy. The genus agrees with Scapholeberh in having the head rounded above and not cari- nate, but differs by having the valves rounded at the junction of the hind and ventral margins. Cerlodaphnia megops, G. O. Sars, large-eyed, as its specific name implies, is distinguished genetically from the two preceding genera by the absence of a rostrum. From C. reticulata (Jurine), the typical species of its own genus, it is separated by not having any row of spinules on the caudal ungues, while from the other congeneric species it is kept apart by theemargina- tion of the caudal region, a space occupied by a series of spines increasing in size as they approach the ungues. In the other direction the caudal margin appears to be serrated or fringed with minute spinules, lessening forward. Among our four species of Chydoridae Eurycercui lamellatus (O. F. Miiller) is pre-eminent in size, in that respect exceeding Simosa vetula of the preceding family, which in lateral view it much resembles. It is easily distinguished by the caudal region, a part which in this species is often strongly protruded from between the valves. The broad blade-like portion between the caudal setae and the emargination that precedes the ungues has its upper or hinder edge prettily serrated. The serration consists of a hundred or more tiny denticles, gradually lessening forward. The genus is separated from other con- stituents of this family by having a pair of small caecal appendages to the front of the intestine, affording an interesting link with the Daphniidae. It is also exceptional with regard to the winter eggs. In all other members of the Chydoridae, with one slight and doubtful exception, the ephippial females are content to deposit a single egg in the so-called ephippium. As is well known to students, the Cladocera produce their young in great numbers parthenogenetic- ally. But, to guard against the total extinction of their progeny through the drying up of the ' Cladocera Sueciae, pi. 23, fig. 2 (1900).
- Journ. Quckelt Microsc. Club, 309 (1900). ' Loc. cit. 3 1 1.
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