4 FOSSIL CIRRIPEDIA. 



resemblance in mere outline. The peculiar cancellated structure, which is almost visible on 

 the external surface even to the naked eye, is wholly unlike anything known amongst 

 Cirripcdia ; a thin polished slice of the valves of Lepas and of Aptychus, viewed under a high 

 power, are as unlike as anything can well be.^ In Aptychus the lines of growth are 

 conspicuous on the inner or concave surface, and indistinguishable or not plain on the 

 outer surface ; whereas in Lepas exactly the reverse holds good. Again, in some 

 specimens it appears, that additions are made to the shell on the exterior edge of the 

 growing margin, instead of on the inner edge, as in Cirripedia. In Aptychus latus, 

 there is a rather deep internal fold along the whole of that margin, through which the 

 cirri are supposed to have been protruded, and this is unlike anything which I have met 

 with in Cirripedes. In all the species of Aptychus, the two valves are much the most 

 frequently, though not invariably, found widely opened, and attached together, either 

 exactly or nearly so, by the two margins through which the cirri must have been protruded. 

 Now in all true fossil pedunculated Cirripedes, the valves are found either separate, which 

 is the commonest case, or when held together, those on the opposite sides almost exactly 

 cover each other, for there is nothing in the structure of Cirripedia tending to open the 

 valves like the hgament in bivalve shells. How comes it, then, that the specimens of 

 Aptychus, even those found within the protected chambers of Ammonites, thus generally 

 have their valves widely gaping ? Even if we pass over this difficulty, is it not strange 

 that the valves should always have been held together by that margin, which in the recent 

 condition is supposed to have been open for a considerable portion of its length, for the 

 exsertion of the cirri ; whereas, in not one single instance, as far as I have seen, are the 

 two valves held together by the opposite margin, which in the recent state, on the 

 idea of Aptychus having been a Cirripede, must have been continuously united by 

 membrane. 



There is another argument against Aptychus having been a Cirripede, which will have 

 weight, perhaps, with only a few persons : in Pollicipes, the main growth of all the valves 

 is downwards ; in Lepas or Anatifa, as well as in most of the allied genera, the main 

 growth of the Scuta and of the Carina (^. e. lower lateral, and dorsal, or valves,) is in a 

 directly reversed direction, or upwards. Now PoUicipes is the oldest known genus of 

 Cirripedes, having been found in the Lower Oolite, whereas hitherto Lepas is not 

 certainly known to have been discovered even in the newest Tertiary formation. So again 

 within the limits of the genus Scalpellum, I know of only two cretaceous species in which 

 the Scuta grow upwards and downwards, and only one case in which the Carina has this 

 double direction of growth ; whereas in the recent and one Miocene species, these valves 

 usually grow both upwards and downwards. Hence it would appear that there is some 

 relation between the age of fossil Lepadidse and the upward or downward direction of 



^ Wlien I had the slices made, I did not know of II. von Meyer's paper on Aptychus, in the 'Acta 

 Acad. C.Tcs. Leop. Car.,' vol. xv, Oct. 182!), tab. Iviii and li.x, fig. 13, in which perfectly accurate sections 

 are given of the microscopical structure of Aptychus Icevis. 



