PETALOCERUS BICORNIS. 275 



hid from view ; the three basal joints are short ; 

 the two terminal ones subequally long, and 

 furnished with a copious brush of strong cilia. 

 These appendages are folded together and en- 

 closed within the branchial chambers, where 

 they, no doubt, fulfil the office of the flabella of 

 the highest forms of Crustacea; affording an 

 interesting illustration of an organ being con- 

 verted, by the force of circumstances, from its 

 original purpose to the fulfilment of another, for 

 which it was apparently most unsuited. 



PETALOCEROS BELLIANUS (WHITE), Proc. Z. S. 1856, 

 p. 134. Between tidemarks, Esquimalt Harbour. 



PETALOCERUS BICORNIS, N. S. Rostrum in duo cornua 

 divisum habens. 



Carapace triangular, anteriorly produced into 

 two horizontal hornlike processes, tuberculated 

 with nodulated prominences all over the surface, 

 but furnished with a series of large tubercles 

 corresponding in a line with the external margin 

 of the carapace ; the antero-lateral margin, con- 

 stricted between the branchial and hepatic regions, 

 furnished posteriorly to the orbit with two strong 

 blunt processes, and posteriorly to the central 

 constriction; armed laterally with two distinct 

 narrow processes, and posteriorly with six closely- 

 situated large round tubercles. 



T 2 



