XCviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 896, 



a very deep, nearly vertical, cylindrical burrow : this goes down 

 for several feet into the sand, which is hardened by the pressure 

 of the dorsal surface of the animal's body. They thus, too, often 

 escape capture by collectors in the living state, and are too delicate 

 to preserve well when fossil. 



2. The Schizopoda, — represented at the present day by Mysis, 

 and numerous other allied genera, — occupy the most primitive 

 position in the order Podophthalma, and still retain unchanged 

 the original characters which distinguished the progenitors of the 

 group in earlier times. 



This is further emphasized by the fact that many Decapod Crus- 

 tacea, in their more-advanced larval stages, pass through a ' Mysis- 

 stage ' before reaching the adult condition. 



Eight pairs of similarly- formed thoracic limbs are present (namely, 

 three pairs of maxillipeds, and five pairs of posterior appendages), 

 each being furnished with a well-developed exopodite and endo- 

 podite, and frequently bearing freely-projecting external gills, not 

 covered by the cephalothoracic shield. 



Considering the greater simplicity of the forms in this division, 

 it seems highly probable that some of the earliest Macruran Crus- 

 tacea, such, for instance, as the Palceocrangon socialis of Salter, 

 from the Coal Measures of Fifeshire, may have belonged to the 

 Schizopoda, but very few of these are sufficiently well-preserved to 

 render exact determination possible. 



Such forms as Udorella Agassizi, Oppel, from the Lithographic 

 Slate of Kelheim, Bavaria, in which the cephalothoracic shield is short, 

 and the legs uniform and provided with endopodite and exopodite, 

 may, I think, with almost absolute certainty be referred to this 

 division. 



Macrura. — The earliest example known of this modern division 

 of Crustacea was obtained by Prof. R. P. Whitfield, in 1880, from 

 the Erie Shales (Upper Devonian), Le Roy, Lake Co., Ohio, U.S.A., 

 and named by him Palceopdloemon Newherryi, which in its general 

 characters closely resembles the modern Crangonidea, the Shrimps 

 and Prawns. 



To this division must also be referred the Palceocrangon esTc- 

 dalensis of Peach (1880), from the Lower Carboniferous rocks of 

 Eskdale, Scotland. 



Eight species of Anihrapalcemon from the Coal Measures of 

 Scotland and England ; one from Illinois, U.S.A. ; and one from 



