120 T. H. Withers — Some Palceozoic Fossils 



Pollicipes siluricus. Since I have not had the opportunity of 

 examining these specimens, and in view of the various shapes of 

 the plates, I do not wish to throw any douht on their Cirripede 

 nature. It is quite a different matter with regard to their generic 

 determination, and in my opinion the characters shown are quite 

 insufficient for referring them either to Pollicipes or Scalpellum. 



In a recent paper (" Some Cretaceous and Tertiary Cirripedes- 

 referred to Pollicipes " : Ann. Mag. Nat. Hist., August, 1914)1 pointed 

 out that, except in the case of the more modified forms of Scalpellum, 

 it was difficult to determine from separate valves the proper syste- 

 matic position of the fossil. This is evidenced by the fact that Darwin 

 and later authors included in Pollicipes all the forms that could not 

 be referred to Scalpellum, but now that we have better material some 

 have been included in new genera, and others have been shown to be 

 primitive forms of Scalpellum (sensu lata). Judging from the structure 

 of the remaining Cretaceous forms, there are very few that could 

 possibly belong to Pollicipes, and in no case can it be stated positively. 

 This is equally true of the Jurassic species, except that the possibility 

 of their belonging to Pollicipes is more remote, and is reduced to 

 fewer species. It is much more likely that many of the Jurassic 

 and Cretaceous species are primitive forms of Scalpellum, but some 

 probably belong to other genera. Notwithstanding this, it is still 

 advisable to retain the generic name Pollicipes for those Jurassic and 

 Cretaceous species which have been referred to that genus, and are 

 represented by valves insufficient for their more correct determination. 



While it may be true that certain forms existed in the Jurassic and 

 Cretaceous rocks, or even in the Palaeozoic, in which the valves had 

 apical umbones, and therefore like Pollicipes had their growth directed 

 downwards, it does not follow that they belong to Pollicipes. They 

 may even, like Pollicipes, have had a larger number of valves than 

 Scalpellum, namely eighteen to over a hundred, but the fact is that, 

 now we know more of what the complete shell in certain fossil forms 

 was like, we see that the difference lies essentially in the disposition 

 of the valves, not in their number. 



On phylogenetic grounds I consider it to be highly improbable, 

 if not impossible, that the genus Pollicipes, which is probably a poly- 

 phyletic one, and still more Scalpellum, could have existed in 

 Palaeozoic times, and it is not sufficient to produce a valve with an 

 apical umbo to prove the existence of Pollicipes. It is necessary 

 to piece together the greater part of the capitulum before we can gain 

 any idea of the affinities of any form. Apart from this, however, the 

 valves hitherto referred to Pollicipes and Scalpellum from Palaeozoic 

 rocks do not even conform to the old conception of the valves of those 

 genera, for none of the valves has a structure closely approaching 

 even the Jurassic and Cretaceous forms. 



TuRRiLEr-AS, H. Woodward, PLtrMtiLiTEs, Barrande, 

 Lepidocoleus, C. L. Faber, and Strobilef-as, J. M. Clarke. 

 Since Dr. H. Woodward 1 referred the fossil from the Wenlock 

 Shale of Dudley, originally described by de Koninck as Chiton 



1 H. Woodward, Quart. Journ. Geol. Soc. London, vol. xxi, p. 486, 1865. 



