E. A. Newell Arber — Culm-measures of Exeter District. 495 



side ' a low boss-like swelling situated obliquely '. The agreement is 

 sufficiently close to put beyond doubt the affinity, already suggested, 

 between Pleurocaris and Acanthot.elson. 



I am indebted to Dr. Henry Woodward for calling my attention to 

 an additional specimen of Pleurocaris in the British Museum collection 

 (I 14449) from the same locality as the type-specimens. It differs 

 from these, not only in its larger size (the total length when complete 

 cannot have been much less than 30 mm.), but also in being relativeh T 

 much wider, measuring 10 mm. across the widest part. This increase 

 in width is due to the greater size of the thoracic pleural plates, which 

 extend on each side for a distance nearly equal, in the middle of the 

 thorax, to the transverse diameter of the somites themselves. It is 

 probable that the increased size of the pleural plates is merely 

 a character of maturity or of age, and that it does not indicate 

 a distinct species. 



1 



III. — The Culm-measures of the Exeter District. 

 By E. A. Newell Arber, M.A., F.G.S., Trinity College, Cambridge. 



N the interesting paper, by Mr. P. Gf. Collins, on the so-called 

 Culm-measures of the Exeter district, which has recently appeared 

 in the last number of the Quarterly Journal,' there are to be found 

 certain conclusions which can hardly pass unchallenged. When this 

 paper was read at the Geological Society, I happened to be in the 

 extreme west of Ireland, and thus, unfortunately, I was unable to be 

 present at that meeting or to take part in the discussion. In fact, 

 it was not until my return to Cambridge in September that I knew 

 anything of the substance of the paper, beyond the very small 

 contribution on the fossil plants which I wrote for it some time ago. 



The chief value of this paper lies in the records of the Carboniferous 

 fauna from South Devon. I must, however, take exception to the 

 author's chief conclusions. 2 Mr. Collins remarks that " comparing 

 the list of South Devon forms with that of the fauna of the ' Pendleside 

 Series ' and that of the Carboniferous Limestone as tabulated above, 

 we cannot fail to be impressed with the great resemblance of this 

 fauna to that of the 'Pendleside Series'". Also that "the 

 fossils, however, described in the present note, support for South 

 Devon what Dr. Hind has stated to be the case in JSTorth Devon, 

 namely, that the Lower Culm-measures are the homotaxial equivalents 

 of the 'Pendleside Series' of the Midlands". Whether or not the 

 scanty flora mentioned in the paper is intended to be included in these 

 conclusions is not self-evident, but I wish to take the opportunity of 

 pointing out that the rocks from which the few fragmentary plant 

 remains there recorded were obtained, are beyond question of Upper 

 Carboniferous age. 



It is quite clear that, both as regards the plants and the fauna, 

 Mr. Collins has failed to recognize the important fact that rocks 

 belonging to both the Upper and Lower Carboniferous series occur 



1 Quart. Journ. Geol. Soc, vol. lxvii, pt. iii, p. 393, 1911. 



2 Ibid., pp. 411, 413. 



