150 BALANID.E. 



projecting longitudinal ribs, the duct curves a little round 

 each rib ; so that the whole duct is formed by as many 

 short inwardly curved portions as the walls have ribs, or 

 longitudinal septa. Between the basal extremities of these 

 parietal, longitudinal septa, the extremities of the radiating 

 septa of the basis project and enter; and along the crests of 

 the latter, little branch-ducts [t), proceeding from the cir- 

 cumferential duct, extend. In the basis, beneath the tubes 

 formed by the just-mentioned radiating septa, there is a 

 cancellated shelly mass (which, in fig. 4 a, was of unusual 

 thickness), and along the crests of the branching ridges 

 forming this cancellated mass, the sub-branches of the above 

 branch-ducts (i f ) run ; these soon become so minute as not 

 to be distinguished by the highest powers, and thus form 

 a sheet of cement, which attaches the last-formed zone 

 of the shelly basis to the sup porting surface. At what point 

 the membrane forming any one duct ceases, the cement- 

 tissue being alone left, I was not able to ascertain ; but the 

 lower parts of the reticulated slip (z, z, fig. 4 a) closely re- 

 sembled the cement-tissue which surrounds the disc-segment 

 of the pupal antennae in Lepas australis. The circumferential 

 duct, here and there, forms little loops, as may be seen in 

 fig. 4 a : and often two branches, running along the crests 

 of two adjoining basal septa, proceed from a common point 

 of the circumferential duct. The cement itself, under dif- 

 ferent parts of the basis, appears as little separate discs, as 

 threads, globules, and as a fine network, but most com- 

 monly as simple layers. As each thick zone of shelly 

 matter is added round the basis, the exterior branches 

 oi' the ducts, between the circumferential duct and the 

 new layer of cement beneath, are fairly imbedded in shell, 

 and are for ever hidden, without, indeed, acid be used for 

 the dissolution of the calcareous matter: so, also, the pre- 

 existing ducts and glands, and the main trunk, would all 

 have been hidden, if the layer of calcareous matter, which, 

 I believe, is thrown down at each period of growth over the 

 entire surface, had not been of excessive tenuity. 



I cursorily examined the cementing apparatus in Bed anus 



paleatu8, improvism and crenatm, which have all calcareous 



\ses } and belong to different sections of the genus \ and 



