206 MR. LUBBOCK ON SOME FRESHWATER ENTOMOSTRACA. 
to look at some nearly dried-up pools of stagnant water, when 1 was delighted to find 
them occupied by great numbers of this interesting species. Still Lepidurus productus, 
though not often met with, has been so well described that I should perhaps not allude 
to it, but that among the specimens I collected there are a considerable number of 
males, while, so far as I am aware, the female sex is the only one which has hitherto 
been met with. My specimens differ in some points from the descriptions and figures 
given by preceding authors. 
Schiffer (* Abhandlungen von Insecten, erster Band, p. 182, pl. 7), who was the first 
to describe this species, had before him, as he expressly says, only young specimens. 
The form of the caudal lamella, however, changes with age, and consequently the figures 
given by Scháffer and copied by Latreille (Hist. Nat. des Crust. et Insect. vol. v. p. 28) do 
not correctly represent the form which is characteristic of mature specimens. The figure 
given by Milne-Edwards (Hist. Nat. des Crust. pl. 35. fig. 5) represents a full-grown (or 
nearly full-grown) individual; but the form of the caudal lamella is not quite correct; at 
least in my specimens it is more regularly oval, the base being narrower, and the 
extremity sometimes entire, sometimes notched, as in the figure. 
Dr. Baird, in his * Monograph of the Apodide”’ (Proc. Zool. Soc. 1852 ; Ann. & Mag. 
Nat. Hist. 1854, vol. xiii. p. 221), describes three species of the genus, and uses as one 
of his specific characters the extent to which the body of the animal is covered by the 
carapace. My specimens, however, varied a good deal in this respect; in some of them 
the carapace left the seven posterior segments uncovered, while in others of the same 
size it extended to the base of the caudal sete, and in one it even covered a large part 
of the caudal lamella. The carapace, however, in all my specimens covered a larger 
portion of the body than appears to be the case in either of the two other species. 
I mention these differences because they show that both the form of the median 
caudal lamella, which changes with age, and the relative size of the carapace, which 
appears to vary so much in different animals, are characters which, though very useful, 
must be employed with great caution in the establishment of new species. 
Both Schäffer (Z. c. pl. 2. fig. 5¢) and Baird (British Entomostraca, pl. 1. fig. d) repre- 
sent the “triangular” plate of the anterior legs in Apus as rounded at the upper end, 
whereas in my specimens of Lepidurus it was pointed. The “rami” have a series of 
notches on each side, which give an appearance of joints. The longest filament has 
about twenty notches on each side, the second about fourteen, and the third only eleven, 
while in Apus cancriformis the two longer rami are described as having respectively 
about sixty and fifty segments. 
On the other hand, as if to counterbalance the shortness of the anterior pair, the 
following legs are decidedly longer and stronger in Lepidurus productus than in Apus 
cancriformis. The pseudosegments, however, even of the longest appendage are not 
more than ten in number. Schiffer and Baird agree in representing the two terminal 
appendages of 4. cancriformis as being nearly equal in size. In L. productus the outer 
one is much smaller, unjointed, broad below, and contracted above. 
In the following legs the triangular plate and the oval appendage become gradually 
larger, while the other appendages become shorter and broader, with the exception of 
