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A. Alcock— New Species of Oxyrhynch Crab. 
[No. 2, 
exception of those belonging to the Regular system, ought to polarise 
light. But this could not be verified in the case of crystals opaque to 
light. There is no such difficulty with electric rays, for all crystals are 
transparent to them. As a matter of fact, all the above experiments 
with one exception were performed with specimens opaque to light. 
Explanation of the plate 
R. ..metallic box containing the Ruhmkorff’s coil. 
S. ..position of the sparking balls. 
L...position of the convex Lens. 
P...the Polariser. 
I... Iris diaphragm. 
K...the Crystal. 
A...the Analyser. 
C... the Coherer. 
G... the Galvanometer. In practice the Galvanometer is placed 
at a greater distance and the leading wires enclosed in 
tin-foil. 
Description of a New Species of Oxyrhynch Grab of the Genus Parthenope. 
—By A. Alcock, M. B., C. M. Z. S., Superintendent of 
the Indian Museum. 
[Read 3rd July.] 
The species here described is a true Parthenope as delimited by 
Miers, Journ. Linn. Soc., Zool., Yol. XIY. 1879, p. 668. 
' Parthenope investigatoris, n. sp. 
Carapace almost equilaterally triangular, the sides very slightly 
curved: its surface is deeply eroded and rugose as in P. horrida and 
spinosissima , but is almost devoid of the sharp tubercles found in 
those species : the antero-lateral borders are slightly crenulate: the 
produced postero-lateral angle is rounded and nearly smooth : the 
posterior border bears five small eroded lobules-a very small one 
in the middle line, with two larger ones on either side-with 
intervening granules. The gastric region is enormously inflated 
as in P. spinosissima , and descends almost vertically to the vertically 
deflexed rostrum, the latter being fused with the interantennulary 
