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POPULAR SCIENCE REVIEW. 
from which the other (terrestrial) classes, with their tracheal 
respiration, have branched off.” * 
Viewed as a whole, the Crustacea probably present to us the 
best zoological illustration of a class constructed on a common 
type retaining its general characteristics, but capable of end- 
less modifications of its parts, so as to suit the extreme require- 
ments of every separate species. 
And it is doubtless in great degree due to this plasticity of 
structure, enabling the species to occupy such diverse positions, 
and to subsist upon such varied aliment, that the class owes 
its preservation through the lapse of ages represented by the 
long series of geological formations, from the Cambrian strata 
to the present day. 
EXPLANATION OF PLATE XC. 
Fig. 1. Pterygotus anglicus, Agassiz, ventral aspect restored. From the 
Devonian of Forfarshire (about one-sixteenth natural size). 
„ 2. Slimonia acuminata, H. Woodw., dorsal aspect restored. From 
the Upper Silurian, Lesmahagow, Lanarkshire (about one- 
ninth natural size). 
„ 3. Stylonurus Logani, H. Woodw., dorsal aspect restored. From the 
Upper Silurian, Lesmahagow, Lanarkshire (about one-half 
natural size). 
„ 4. Eurypterus Scouleri, Hibbert, dorsal aspect restored. From the 
Carboniferous limestone of Kirkton quarry and Bathgate, 
West Lothian (about one-eighth natural size). 
„ 5. llemiaspis limuloides , H. Woodw., dorsal aspect. From the 
Lower Ludlow Leintwardine, Shropshire (about two-thirds 
natural size). 
„ 6. PrestwicJiia rotundata, H. Woodw., Coal-measures, Ironstone, Coal- 
brook Dale (about two-thirds natural size). 
„ 7. Bellinurus Konigianus, IT. Woodw. sp. nov. Coal-measures, Dudley 
Coal-field, in clay ironstone (natural size). 
„ 8. Prestwichia Birtwelli, H. Wood. sp. nov. Coal-measures, Corn- 
field Pits, near Padiham, Lancashire (natural size). 
„ 9. Neolimulus falcatus, H. Woodw. Upper Silurian Lesmahagow, 
Lanarkshire (twice natural size). 
„ 10. Dithyrocaris Scouleri, McCoy, Carboniferous, Ireland (one-fifth 
natural size). 
„ 11. Larva or Zoea of the common “ Shore-crab,” Carcinus mcenas> 
Penn. 2nd stage, copied from Mr. C. Spence Bate’s paper on 
the 11 Development of Decapod Crustacea,” Phil. Trans. 1858, 
p.589, PI. XL. 
* 11 Facts and Arguments for Darwin,” by Fritz Muller (p. 120). Trans- 
lated from the German by W. S. Dallas, F.L.S., &c. 
