from the Silurian Rocks. 155 



A further exploration in the same rich deposits at Lesmahago, 

 where Ceratiocaris occurs in millions (and in these beds no other 

 fossil has yet been brought to light), has disinterred the rostrum *, 

 hard jaws, and also the antennas or some of the thoracic ap- 

 pendages of the animal. The last are obscure, but were 

 detected by Prof. Huxley, who also found a clearly articulated 

 hinge uniting the two flaps of the carapace. This is a very 

 important character, and will remove Ceratiocaris from any 

 very near alliance with Nebaiia, from which also the solid jaws, 

 like those of Apus, and the greatly developed telson, often 

 three times the length of the other caudal appendages, tend 

 further to separate it. In Nebaiia the telson is reduced to 0, 

 and the appendages are large. 



The length of the largest Ceratiocaris yet known could not 

 have been less than 15 inches. The characters of the genus 

 may stand as follows : 



CERATIOCARIS, M'Coy, 1851. 



Carapace bivalved, united by an articulated hinge ; the valves 

 ovate, semiovate, or subquadrate, mucronate or uncinate in front, 

 and more or less truncate behind. Rostrum broad, of a single 

 lanceolate piece. (Head or thorax with obtuse (jointed?) 

 appendages). Body many- (fourteen- or more) jointed, of which 

 five or six segments extend beyond the carapace ; the last one 

 longest, and supporting a strong bulbous telson and two shorter 

 appendages. Surface generally lineate, often finely so. 



1. C. papilio, S alter. 

 ('Siluria/ 2nd ed. 1859, p. 262. f. I, 2.) 



C. 3-4-uncialis, cephalothorace magno, abdomine breviore. Cepha- 

 lothorax tenuissime striatus, oblongus, antice latior. Annuli cor- 

 poris numerosi (13 et ultra?), 3-4 ultimi solum liberi, hi quam 

 longi ter latiores, ultimus precedentem quater excedens. Ap- 

 pendices validse, ceutralis (telson) longa paullum recurva, 

 costata, laterales latse. 



This beautiful species occurs with the next, but is less com- 

 mon. The much shorter body scarcely longer (tail included) 

 than the great carapace easily distinguishes it. We have spe- 

 cimens both with the valves open and closed; and it is this 



* The part /(fig. 3), supposed to be analogous to the rostrum in Nebaiia 

 (see Gaimard, Voyage Scandinav. 1845, pi. 40. f. 2 b) is generally joined to 

 the carapace of the fossil. It is very closely and beautifully striate, V- 

 fashion, from end to end. It occupies the place where the antennae might 

 be expected to occur, but is only a single piece. My friend Dr. Kinahan 

 of Dublin suggested that it might prove to be the rostrum j and I fully 

 agree with him. The striatiou favours this view materially. 



11* 



