CRUSTACEA.. 
61 
faintly grooved near their distal extremities, but in the usual condition of 
preservation as casts of the lower surface, the tendency to duplicature is not 
often apparent. Doublure narrow on the sides, rapidly widening toward 
the posterior spine, where it extends foiuvard as far as the termination of the 
axis. The caudal spine is not infrequently broken away from the margin of 
the doublure, giving the caudal shield a semicircular outline. 
Surface Ornamentation. The surface of the cephalon, within the border and 
the occipital ring, is covered by strong tubercles, which are closely disposed 
over the cheeks and more scattered on the glabella. In old individuals these 
tubercles extend to the margin, and the orbital ridge of the cheek becomes 
covered with fine granulations. The surface of the thorax and pygidium is 
smooth or finely granulose. Pygidia of young individuals show low nodes or 
tubercles upon the pleurae, apparently arranged in three or four oblique rows 
with indications of similar ornamentation upon the axis. 
Dimensions. The only specimen observed which retains the parts in con¬ 
junction affords the following dimensions, proper allowance being made for 
the caudal spine which is lost. 
Body. Cephalon. Thorax. Pyg-idiuin. 
Length_ 103 mm. 25 mm. 40 mm. 38 nim. 
Width- 49 mm. 49 mm. 50 mm. 39 mm. 
The smallest head-shield observed has a length of 9 mm., and a width of 
. 16 mm., and the largest, which can safely be referred to the normal form of 
the species, a length of 35 mm., and a width of 70 mm. Pygidia vary in 
size from a length and width of 15 mm., to a length and width of 110 mm. 
Vaeiations. Large cephalic shields associated with Dalmanites anchiops and 
bearing all the essential specific features of the normal form, afford some 
important varietal differences. One series of these variations has been 
already described under the first of the following designations. 
