DECAPODA. 5 
included) the Arctic regions of the Atlantic and Pacific. The question has been 
discussed by Dr. Ortmann,* who concludes that C. antarcticus is specially and closely 
related to the Californian C. franciscorum, Stimpson, and that its presence in the 
Southern Hemisphere is to be explained by migration from the North along the West 
coast of America, where the hydrographical conditions are such as to favour an inter- 
mixture of northern and southern faunas across the tropic zone. 
With a view to testing this conclusion of Dr. Ortmann’s, I have carefully compared 
the specimens of C. antarcticus with specimens of C. franciscorum in the Museum 
collection.t The chief character on which Dr. Ortmann relies for linking the two 
species together is the presence of a pair of dorso-lateral spines on the hind margin of 
the fifth abdominal somite. This character is conspicuous and definite, but it may be 
doubted whether it is of great morphological importance. Prof. Sars figures a pair 
of spines of varying length in nearly the same position in all the larve of Crangonide 
examined by him,{ and it seems likely that this larval character may have been 
retained independently in species not closely related. In other respects C. franciscorum 
differs considerably from the Antarctic species. The surface of the carapace is much 
less uneven, the various ridges and hollows being much less strongly marked. There 
is no ridge running backward from the median dorsal spine, and the ridge connecting 
the antennal and hepatic spines is interrupted by a groove. The pterygostomial spine 
is not compressed and expanded laterally as it is in C\ antarcticus. The rostrum is 
shorter than the eye-stalks, depressed and hollowed on the dorsal surface and bluntly 
pointed. The sixth abdominal somite is about one-seventh of the total length, and has 
only a faintly-marked indication of a double keel on its dorsal surface. The telson 
narrows gradually to an acute tip. The antennular peduncle is stout, the distal end of 
the first segment broader than three-fourths of the greatest diameter of the eye; the 
outer lobe of the first segment has its external margin strongly bent upwards, thickened 
and produced forwards into a strong spine which reaches the distal end of the segment. 
The outer edge of the antennal scale is slightly convex. Miss Rathbun states 
(Harriman Alaska Exp., Crustacea, p. 120) that the third maxillipeds do not reach the 
end of the antennal scale, but in two out of three specimens examined by me 
they certainly do so. The first legs reach the tip of the third maxillipeds ; the 
palmar edge of the hand is very oblique, its terminal tooth being more than one-third 
of the length of the hand from the distal end. The last pair of legs reach to 
about the middle of the antennal scale, The first pleopod differs considerably in shape 
from that of C. antarcticus, the endopod being attached nearly half-way down the inner 
margin of the peduncle. 
* Jenaische Denkschr., VIII. (Semon’s Zool. Forschungsreise V.), (1) (1894), p. 77; Proc. Acad. Nat. Sci., 
ilad., 1895, p. 190; Zool. Jahrb., Syst. TX. (1897), p. 582. 
es ee These pegniene received fron the Smithsonian [nstitute, are labelled as having been collected in 
California by Stimpson himself, in the course of the North Pacific Exploring Expedition, and may therefore Le 
ded as co-types. 
ee Bidrag al Kundskaben om Decapodernes Forvandlingar, iii, Fam. Crangonide. Arch. Math. Naturvid. 
xiv. (1890), pp. 182-195, pls. i—vi. 
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