Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume VIII (1888-1891)
Birge, Edward A.
List of crustacea Cladocera from Madison, Wisconsin , pp. 379-Plate XIII ff. PDF (7.9 MB)
Lest of Crustacea Cladocera from Madison, Wis. 389 -lakes are only a mile apart, I have not found the pointed variety in Mendota or the rounded in Wingra. The outlines of the head are very -variable, the variations quite closely resembling those represented in -D. berolinensis, apicata, and eucullata, although of course this species has I i the macula nigra. The males appear in the latter part of September. The flagellum of the antennule is convex stout and short, usually little longer than the sense-hairs. The anterior sense-bristle in our specimens lies little nearer -the end of the basal portion of the antennule than the head. In this our specimens differ from Eylmann's * description, who says of it, that it is "von der Endborste nicht weit entfernt."' This species is the most abundant in the open waters of the Madison lakes. I have also obtained it from Minnesota and Michigan, showing some variation from our form in each case. Species 24. D. KAHLBERGENSIS var. RETROCURVA, Forbes. Plate XIII. Figs. 7, 8. This form was first described by Forbes * as a distinct species. It is the Most extreme Daphnid form yet observed. I cannot agree in the state- ment of Forlbbsthat the large helmeted forms predominate in the smal- ler lakes (I. c. p. 643.) At Madison the forms of D. hyalina and of D. retrocurva in Lake Mendota are much more helmeted than those in Lake Wingra. The former lake is about six miles by four, the latter 1-4 by 34 mile. D. hyalina in the smaller lake is more like D. apicata, while in Mendota the crest is more developed than is shown by any iEuropean descriptions. D. kahlbergensis from Wingra shows the forms typical of that species and of cederstroemii while the full development o f t__ e - c r e s t - o n l y - c o m c s - i u t h e u r l kE . T - m e M s _ss Us i e - p pear late in the fall, in the latter part of October and in November. The head is of the kahlbergensis type, sometimes curved up but never showing the extreme development of the female. The antennule has a flagellum a good deal longer than the sense-hairs, curved at the tip and distinctly articulated to the basal part. Our specimens do not show the extreme development of the head be- fore birth noted by Forbes (1. c., p. 642). The head in the young is not as much crested as in the adult D. hyalina. This species is always found -in company with D. hyalina and is far less numerous. On calm summer -nights the water of Lake Mendota swarms with these two species, to- gether with a Cyclops, a Diaptomus, and Leptodora hyalina. They are not abundant close to shore and seem to spend the day in swarms at the * Eylmann, E. Beitrag zur Systematik der Europiischen Daplniden, Freiburg i. B. 1886, p. 33. * Forbes, S. A. Entomostraca of Lake Michigan and adjacent waters. American Natur- alist. Vol. xvi., p. 642, August, 1882. M-W ; - L. I ;, l I i I I I 4 11 I a L
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