DITHYROCARIS INSIGNIS. 161 



edge to the mesolateral ridge ; the latter is strong, and the former has a simple 

 fringe as in other species (for instance, fig. 3 a, PL XXVIII). The ornament of 

 the surface consists of simple oblique strias, parallel, but interrupted, with 

 punctate interspaces, and probably passed into meshwork on other parts of the 

 test. The specimens from Eccup occur in a hard, dark-blue, non-calcareous shale, 

 with Posidonomya, Aviculopecten, Goniatites, &c. 



Leeds Mus. Coll., No. 39 b. 



This is a small right valve of D. insignis, 43 mm. long and 20 mm. wide ; from 

 the dorsal to the mesolateral 10 mm., and the same from that to the ventral. A 

 neat ogee curve in its front edge resembles that in fig. 3 a, PI. XVIII ; and figs. 

 1 and 2, PI. XXIV, have a similar feature. 



The superficial ornament is a freely irregular reticulation coming off from the 

 oblique lines crossing the ridges. 



PI. XXX, figs. 1 and 2 a, b. Leeds Mus. Coll., No. 33 a. 



Characters and Size. — Two valves displaced ; the right valve, turned over, has 

 left the impression of its outside (fig. 1) ; the outside of the other is exposed 

 (fig. 2 a). 



Fig. 1, the impression of the outside of an imperfect right valve, 73 mm. 

 long and 35 mm. wide. It shows a thick ventral rim and a strong mesolateral 

 ridge. The posterior border, with its spines, ventral and dorsal, is well indicated, 

 but the spines have been damaged. 



Fig. 2 a is the outside of a left valve, 71 mm. long and 37 mm. wide. The 

 mesolateral ridge is prominent and rugose as usual; the dorsal ridge is feebly 

 crested. The gastric and nuchal ridges are in their places. The ventral border 

 is broad and thick, and does not show any fringe. 



PI. XXX, figs. 3 a, b, c, d, e. Leeds Mus. Coll., No. 44a and 44b (counterparts). 



Size. — Length of carapace, with the spines (10 mm.), 60 mm. ; width 50 mm. 



Character. — A nearly perfect suborbicular carapace, somewhat damaged 

 anteriorly. Ventral border broad ; much obscured by being inturned and broken. 

 A little portion of the usual fringe is traceable on the counterpart (not figured) ; 

 the different patterns of the inside and outside free edge of the ventral margin 

 can be seen both in it and in fig. 3 a. The postero-ventral spines are long and 

 sharp. Mesolateral ridges rugose and strong, especially shown by deep furrows 

 on the counterpart, in which a gastric tooth projects at the front end of the right- 

 hand mesolateral. The dorsal ridge is relatively weak, but ends behind in a 

 distinct triangular spine (4 mm. long). 



The ornament of the surface near the mesolateral consists of sinuous, parallel, 



