Notes on Species of Ceratiocaris. 395 



wards and backwards, to about the middle of the ventral margin, 

 where the valve is deepest (highest) ; and 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 specimen M. P. G. x -iV. The outline is often 

 modified by pressure in other positions ; but not to quite so great an 

 extent, as the shape of C. 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 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, coming from 

 angular imbricated lines on the back (as in C. Scharyi, Barrande, 

 and C. Deioeii, Hall). The joints are sometimes more than twice as 

 high as long. The last one is as long as three of the others. The 

 telson is short, and is apparently in some cases about half as long 

 again as the stylets (as 50 is to 30) ; and some specimens show 

 traces of thin cestui £e, and perhaps of prickles. The whole adult 

 animals were from 4 to 8 inches long. 



Specimen M. P. G. x ^V has the rostrum and teeth squeezed out 

 loose near the front end. A large individual, Cambridge Mus. 

 &/65, measures — 



Carapace . . • 83 x 55 mm. 



Four segments . 40 ) ^, 



T * ^ » } o'5 mm. 



l^ast segment . . 25 j -^ 



Telson . . . • 5° ,, 



198 mm. or nearly 8 inches. 

 A small specimen, M. P. G. x ^V? nieasures — 

 Carapace . . . 40 x 26 mm. 



Four segments . 20 ) -, 



T ^ ^ . -, MO mm. ? 



l^ast segment . . ? 10 ) ^^ 



Telson .... 30 ,, 



About 100 mm. or nearly 4 inches. 



C. stygia was rather larger than C. papilio ; its telson was larger ; 

 the carapace was markedly distinct by its trapezoidal outline, deep 

 ventral region, and mucronate antero-dorsal angle, which was not 

 nearly so often lost in fossilization as the front angle of C. papilio. 

 In its rostrum, teeth, superficial ornament of carapace and of body- 

 rings, it seems to have closely resembled C. papilio. In ten good 

 specimens from Lesmahago, two are simple carapaces ; three have 

 body-segments in places, and five have them shifted or reversed. In 

 this respect C. stygia seems to have been rather less liable to the 

 dissolution of the membranous attachments of the body than its 

 associate C. papilio. 



A postero-dorsal fragment in Cambridge Museum (Marr Coll.), 



