668 



ARTHROPODA 



SUB-KINGDOM VII 



Sub-Order A. AMPHIPODA. Latreille. 



Body laterally compressed, with gills borne on the bases of the walking feet ; abdomen 

 elongate, the three anterior feet natatory, the rest posteriorly directed and saltatory. 



The Amphipods, or beach fleas, are mostly small, aquatic animals, and generally 

 marine. They live in shallow water between rocks, beneath seaweed, etc., or in some 

 cases in tubes or burrows constructed by themselves. They leave 

 tracks upon the surface of mud and sand which resemble the 

 Palaeozoic Nereites. Fossil remains are extremely scarce, and are 

 derived chiefly from fresh-water strata. 



A few Palaeozoic forms have been described under the names 

 of Necrogammarus Salweyi, "Woodw., from 

 the Ludlow beds ; Diplostylus Dawsoni, 

 Salter, from the Carboniferous of Nova 

 Scotia; Palaeorchestia, Zitt. (Fig. 1405), 

 from tlie Coal Measures'; and Bostrichopus, 

 Goldf., from the Culm Measures of Herborn. 



FIG. 1405. 



ures ; Lisek, near Beraun, 

 Fri?sch). ia ' r 



FIG. 1406. 



These are all problematical forms of doubtful Gammams Oenir 



-,,.,. T , . . .. ... Heer. Miocene; Oenin- 



relationships. Less uncertain in its position geU) Baden, a/j. 



is Acanthotelson, Meek and W., from the Carboniferous of Illinois, 



which, although raised by Packard to ordinal rank (Syncarida, see above under 



Schizopoda], shows no features incompatible with Amphipod 



relations. The few Tertiary forms, such as Gammarus, Fabr. 



(Fig. 1406) ; Typhis, Risso ; and Palaeogammarus, Zadd., closely 



resemble living types. 



Sub-Order B. ISOPODA. Latreille. 1 



Body depressed, usually broad, flat below, rounded above: 

 with seven free thoracic segments, and no strongly developed 

 carapace. Gills borne on the lamellar appendages of the abdomen, 



which is short-ringed and 'often reduced, its 



segments partially fused. Caudal segment 



relatively large, shield-shaped. 



Most Isopods are marine, frequenting 



the coast ; a few inhabit fresh water, and 



about an- equal number (Oniscidae) live in 



moist terrestrial localities. Of the some- 

 what rare fossil remains, Praearcturus, 



Woodward, is a large form from the Old 



Red Sandstone of Herefordshire ; Amphi- 



peltis paradoxus, Salter, occurs in the 



Devonian of Nova Scotia ; Arthropleura, 



Jordan, is found in the Coal Measures ; 



Urda, Minister (Fig. 1407), in the Litho- (after Woodward). 



graphic Slates ; Archaeoniscus, M. - Edw. 



(Fig. 1408), in the English Purbeck ; 

 1 Literature : 



Milne-Edwards, H., Sur deux crustaces fossiles (Ann. Sci. Nat. Zool. [2], XX.), 1843. On 

 Archaeoniscus (Ann. Mag. Nat. Hist. [2], XIII.), 1844. Meyer, H. v., Ueber Palaeoniscus obtusus 

 ( Palaeontogr. , V.), 1858. Kunth, A., Crustaceen von Solenhofen (Zeitschr. deutsch. geol. Ges., 

 XXII.), 1870. Woodward, H., Several papers on British Fossil Isopods in Trans. Woolhope Field 

 Club, 1870 ; Geol. Mag., VII., 1870 ; [3], VII., 1890 ; [4], V., 1898 ; and Quar. Journ. Geol. Soc., 

 XXXV., 1879. Ammon, L. v., Beitrag zur Kenutniss der fossileu Asseln (Sitzungsber. Bayer. Akad. 

 Wiss.), 1882. Carter, J., On Fossil Isopods (Geol. Mag. [3], VI.), 1889. 



Pic. 1407. 



Urda rostruta, Mlinst. 

 Lithographic Slates ; 

 Solenhofen, Bavaria. 

 l/l (after Knnth). 



FIG. 1408. 

 A, Archaeoniscus Brodei, 



B, Frag- 

 ment of matrix, Vi (after 

 Quenstedt). 



