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 forward 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 hue granulations. The surface of the thorax and pygidium is 

 smooth or finely granulose. Pygidia of young individuals show low nodes or 

 tubercles upon the pleura?, 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. I rax. Pygidium. 



Length 103 mm. 25 mm. 40 mm. 38 mm. 



Width 49 mm. 49 mm. 50 mm. 39 



mm. 



The smallest head-shield observed has a length of '.I 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 1 111 mm. 



Variations. Large cephalic shields associated with Dalmanites anchtops 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. 



