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. Ortrnann's, I have carefully compared 

 the specimens of C. antarcticus with specimens of C. franciscorum in the Museum 

 collection.! 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 larvae of Crangonidse 

 examined by him,J 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. Soi., 

 Philad., 1895, p. 190; Zool. Jahrb., Syst., IX. (1897), p. 582. 



f These specimens, received from the Smithsonian Institute, are labelled as having been collected in 

 California by Stimpson himself, in the course of the North Pacific Exploring Expedition, and may therefore be 

 regarded as co-types. 



J Bidrag til Kundskaben om Decapodernes Forvandlingar, iii. Fam. Crangonidfe. Arch. Math. Naturvid. 

 xiv. (1890), pp. 132-195, pis. i.-vi. 



2 A 



