CERATIOCARIS STYGIA. 39 



Carapace-valves trapezoidal ; back straight, but curving down for a short 

 distance to the mucronate dorsal angle of the anterior edge, which then slopes, 

 with a slight convexity and at a sharp angle, downwards and backwards, to about 

 the middle of the ventral margin, where the valve is deepest (highest) ; the other 

 half of the ventral edge rises slowly with a straight or nearly straight oblique edge 

 to the blunt postero-ventral corner, whence the truncate hind margin rises, with a 

 gentle concave curve, to the sharp postero-dorsal angle. When the valves are 

 spread open a triangular space is left between the antero-dorsal angles. This 

 condition and the shape are well shown in the outspread specimen M. P. G. x -^§. 

 Fig. 2 a is taken from a less trapezoidal specimen. The outline is often modified 

 by pressure in other positions, but not to quite so great an extent, as the shape 

 of G. papilio is altered by squeeze in some instances. The valves are delicately 

 striate, with longitudinal lines curving parallel with the ventral edge, and crowded 

 at the postero-dorsal angles. The lower margin has a slightly thickened rim and is 

 often marked with the bases of former seta3. The body-segments, of which probably 

 five were outside the carapace (though often the segments seem to have been pushed 

 back within the carapace after death), are marked with delicate, raised, oblique 

 wrinkly lines on the sides, and ornamented on the back with a leaf-like pattern, 

 or lattice-work, formed by an imbrication of angular lines, which pass down into 

 the lateral oblique wrinkles. These joints are sometimes more than twice as high 

 as long. The last one is usually as long as three of the others. The telson is 

 apparently in some cases about half as long again as the stylets (as fifty is to 

 thirty) ; and some specimens show traces of thin costulse, and perhaps of prickles. 

 The whole adult animals were from four to eight inches long. 



In both G. papilio and G. stygia the caudal spines are broad and taper quickly ; 

 but the stylets are broader and shorter than the style. In G. stygia the style is 

 usually rather more than twice, and in G. papilio only about twice as long as the 

 ultimate segment. 



Specimen M. P. G. x ^o nas the rostrum and maxillae squeezed out loose near the 

 front end of the carapace. A large individual, Cambridge Mus. &/65, measures — 



Carapace .... 83x55 mm. 



Four segments . . 40 \ fic . 198 mm., or nearly 



Last segment ... 25 ) 8 inches. 



Telson 50 „ 



A small specimen, M. P 



Carapace .... 40x26 mm." 

 Four segments . . 20 ) ™ 

 Last segment . ' . . 10 ? ) 

 Telson ..... 30 



About 100 mm., or 

 nearly 4 inches. 



