122 T. H. Withers— Palaeozoic Fossils. 



Squamula. The above four specimens are therefore some of those 

 which he originally intended to include in Squamula, and they appear 

 to be identical with the plates figured by him (p. 576, pi. xx, 

 figs. 22-4, 1872, especially fig. 22) as Plumulites squamatula, a species 

 recorded from Etage D and E. Their reference to Plumulites was 

 probably the reason for giving up Squamula, but that genus would 

 have been quite justified since Plumulites squamatula undoubtedly 

 belongs to the genus Lepidocoleus, C. L. Faber (1887). Meanwhile 

 the name Squamula has no nomenclatorial validity. 



In Lepidocoleus there are ouly two vertical columns of plates 

 apparently overlapping on the median line, with slight alternation, 

 and the shell is capable of opening along the narrow free edge. 



Turrilepas ( Fig. 7, p. 1 14) and Plumulites (Fig. 6, p. 1 14). These two 

 genera differ from Lepidocoleus in having a. greater number of vertical 

 rows of plates. Of the actual number there is some difference of 

 opinion, but since I am able to state positively that there are only 

 four in Turrilepas, it is probable that there are four rows also in 

 Plumulites. Much misconception has arisen with regard to these two 

 genera, mainly owing to the fact that the structure of them has been 

 misunderstood, with the result that while many species have been 

 distributed between them, some authors give priority to Plumulites 

 and others to Turrilepas. The whole history need not here be gone 

 into, but it is clear that these two genera are quite different. 

 The main difference lies in the two median rows of plates, for while 

 in Turrilepas (Fig. 7) they are keeled or sharply bent longitudinally, 

 and alternate with each other, in Plumulites (Fig. 6) the plates are 

 not keeled, are altogether different in shape, and do not alternate, 

 their inner margins abutting. The plates on each side of the keeled 

 plates in Turrilepas are not minute as described by Dr. Woodward 

 and Professor Moberg, but are about the same size as the keeled 

 plates. They resemble the leaf-like plates in Phimulites, except 

 that they are not so much produced at their apical ends and do not 

 possess a median longitudinal fold. While it is gratifying to note 

 that Professor Moberg in his above-quoted paper, "Om Svenska 

 Silurcirripeder," has recognized the difference between Plumulites 

 and Turrilepas, a view I have held for some time, it may be said that 

 it is not British palaeontologists alone who have confused these two 

 genera. Everyone who has written on these forms has done so, and 

 the authors of the genera even claimed priority each for his own 

 genus, thinking that they were synonymous. But Mr. F. P. Cowper 

 Peed : doubted whether they were synonymous, although they are so 

 regarded even in the last edition of Zittel-Eastman. Professor Moberg 

 conveniently gives on the same plate figures of all the above genera, 

 but, seeing that he distinguishes between Plumulites and Turrilepas, 

 it is surprising to find that he figures, not Plumulites bohemicus, 

 Barrande, 2 which should be regarded as the genotype of Plumulites, 

 a species very like P. peaclii (Fig. 6), but P. folliculum, Barrande, 



1 F. E. C. Eeed, "The Structure of Turrilepas Peaclii and its allies": 

 Trans. Eoy. Soc. Edin., vol. xlvi, pt. iii, No. 21, p. 519, 1908. 



2 J. Barrande, Systeme Silurian Boheme, Supplement to vol. i, p. 569, 

 pi. xx, fig. 1, 1872. 



