part -1] CAMBRIAN HORIZONS OF COMLEVT. 375 



somewhat intermediate between those of the Lower and the Middle 

 Cambrian, but still to be classed with the former. As it is also 

 recorded from Neve's Castle in the Wrekin district, where the Lower 

 and the Middle Cambrian are again in juxtaposition, this bed and 

 its fauna seem of interest as a possible index of the dividing-line 

 between the two formations. Further evidence of a transition, if 

 such ever existed in the district, is lost by reason of the uncon- 

 formity that ushers in the Paradoxidean fauna, which only arrived 

 after a considerable interval. 



The Middle Cambrian faunas have already been indicated in 

 previous publications by me ; the Paradoxides-oelandicus fauna in 

 horizons Ba,, Ba.,, and Ba, ; the P.-tessini fauna in horizon Bb t , and 

 probably higher zones ; the P.-davidis fauna in horizons Bb^ and 

 Bb 3 . 



The brachiopoda now prove the presence of a fauna of 

 Paradoxides-forchammeri age in horizon Be, and the Upper 

 Cambrian age of the Orusia Shales, horizon Ca, at the summit of 

 the sandstone series of Comle}^. 



Certain points of, perhaps, minor importance result from the 

 detailed study of the brachiopoda. The genus Acrothyra appears 

 in the district at the summit of the Lower Cambrian deposits, and 

 its range is extended into the Middle Cambrian. The specimens 

 are in such excellent preservation that it has been possible to deter- 

 mine the forms of the visceral cavity in at least four stages of 

 growth. Micromitra (Paterina) labradorica exhibits some fea- 

 tures of the growth of the adult shell, and was preceded in time 

 in this district by M. (P.) phillipsi. The specimens of Ob ol ell a 

 atiantica in two varieties show the internal characters distinctly. 



I could not have undertaken the study of the Comley 

 brachiopoda without the help of Dr. C. D. Walcott's monograph, 

 which has served as text-book, bibliography, stratigraphical guide, 

 and work of reference, all in one, and I desire to acknowledge 

 the very great assistance which I have received from that com- 

 prehensive work. I am also most grateful to Dr. Walcott for the 

 loan and gift of some American specimens. 



I am also further indebted to Dr. C. A. Matley for the notes on 

 the brachiopoda of the Paradoxides Beds of Comley (1911) : they 

 were almost my first lesson in the study of this group of fossils. 



At the outset of the excavation work at Comley, Dr. T. T. Groom 

 very kindly examined some of the pteropoda. and his preliminary 

 assistance was of considerable value. Grateful thanks are also due 

 and tendered to Prof. W. J. Sollas. for the opportunity of studying 

 the specimens from Malvern that are in the Oxford Museum. Last, 

 but by no means least, I owe an ever-increasing debt of gratitude 

 to the late Prof. Charles Lap worth for much kind advice as to 

 the scope of this paper and for encouragement throughout its 

 preparation. 



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