CRUSTACEA. 171 



Barrande had earlier described and figured similar bodies (Syst. Silur. 

 Boheme, vol. i, Suppl. p. 443, pi. xxi. figs. 41-44. 1872), from the I'lage E., 

 associated with Ceratiocaris, and regarded them as the masticatory organs of 

 individuals of that genus. These mandibles are generally somewhat trian- 

 gular in outline, with sometimes a straight but usually curved or lunate 

 crown. This crown or masticating surface is broad, and bears five, six or 

 seven cuspid denticles, of which those at the extremities are more pointed, 

 simple and canine-like; those between having a surface strikingly similar to 

 that of the human molar. The lower or basal portion of the mandible is 

 broad and in many instances the surface of attachment is somewhat pro- 

 duced behind into the manubrium. The substance of this portion of the 

 mandible is much thinner than that of the grinding surface, and on account 

 of its being often crushed, the manubrium is frequently not apparent, and 

 in young individuals it seems not to be developed. Judging from the 

 relative proportions exhibited in the length of the mandibles, and of the 

 entire animal in E. punctata, the largest of these bodies observed, which has 

 a length of 38 mm., may have belonged to an animal 390 mm., or upwards 

 of fifteen inches in length. 



An individual of 'Ceratiocaris papilio, Salter, has been figured by Woodward 

 (Geol. Mag., vol. ii, p. 501, pi xi, figs. 1. 2), in which the mandibles are visible 

 through the substance of the carapace. They appear to be of the same general 

 character as those here described, but much smaller in proportion to the size 

 of the carapace, and if represented in their normal position, situated much 

 more anteriorly. Woodward's figure indicates that these bodies have under- 

 gone a vertical displacement, as both mandibles are equally distinct in a 

 profile view of the specimen, and it is possible that a horizontal displacement 

 has pushed them forward beyond their normal position. The figures of the 

 mandibles of Dithyrocaris, upon the same plate, taken from a specimen de- 

 scribed by Portlock (Geol. Kept. Londonderry, p. 315, pi. xii, fig. 6. 1843), 

 show some minor differences in form and outline but apparently insufficient 

 to be of value as generic features. 



