182 A HISTORY OF EECENT CRUSTACEA 



calcareo-membranous chamber, attached to the upper wall 

 of the antenna). Around the orifice that opens into it, 

 within the chamber, there is a curved row of closely 

 planted delicately ciliated hairs, each of which is attached 

 to the base by a flexible membranous articulation, from 

 which it proceeds flattened and tolerably broad for more 

 than half its length, when it narrows rapidly and becomes 

 ciliated, the cilia being short and fine ; the hairs extend 

 nearly if not quite across the auditory chamber, the floor 

 of which is covered with small points, while the cavity 

 contains much angular calcareous sand. This I found 

 mostly gathered into a compact mass, but most probably 

 when the animal was in a living condition it was not so, 

 being then kept in a state of motion by the aid of the long 

 slender ciliated hairs that have just been described.' In 

 discussing the peculiar combination of slender filaments 

 and flattened plates in the branchiae of this crustacean, 

 Mr. Spence Bate observes : — ' In a respiratory chamber, 

 such as in the genus now before us, the water flows in by 

 the posterior extremity, for which purpose the carapace 

 can be raised or depressed at will within certain limits ; 

 and as w^e may assume that in a large chamber such as 

 the present, the water flows along the lower margin, pass- 

 ing out at the anterior end only, it is probable that the 

 largest amount of current will correspond with that por- 

 tion of the chamber where the trichobranchiate filaments 

 are best developed and most abundant, whereas the phyl- 

 lobranchial plates are present in the centre and deeper 

 recesses of the chamber, where the circulation will be 

 more quiescent, and the power of oxv^genation less effi- 

 cient.' As there is reason to suppoi^e that the animal may 

 inhabit hollow passages in the mud, where the circulation 

 of water through the branchial chamber would not be very 

 vigorous, and least so in the part most distant from the 

 direct current, Mr. Spence Bate infers that in the central 

 portion of the chamber the branchiae have been developed 

 into thin foliaceous plates of considerable dimensions, so 

 that through the tenuity of their structure the blood may 

 be brought over a large surface into contact with the 

 aerating medium within the chambers. 



