Revieivs — Magnetic BiHturhonces. 133 



rocks containing Pecten asper are always recognized as marking 

 the base of the Cenomanian." It served to emphasize the 

 fact that the P. asper-zone is Cenomanian, that Jukes-Browne 

 invented the term " Selbornian " for the Albian (including the 

 zone of Mortoniceras rostratum) plus the P. asper-zone of the 

 Cenomanian, for convenience in writing of the Upper Greensand 

 of the South- West of England. Incidentally Jukes-Browne, not 

 recognizing the zonal name as a mere label, quite unnecessarily 

 altered the name of the zone from P. asper to Cardiaster fossarius, 

 on the ground that P. asper was not commonly found in Devon 

 and Dorset. 



It might be sup^^osed from a perusal of this work that in order 

 to study the Cretaceous Sponges of North- West Germany, it is 

 necessary to visit the collection in the American Museum of Natural 

 History. But the British Museum possesses a very large collection 

 of these sponges, named by Dr. Schrammen, and purchased from 

 him some eighteen years ago. Specimens from this collection are 

 figured on plate iii of the British Museum Guide to the Fossil 

 Invertebrate Animals, a circumstance not noticed by Dr. O'Connell. 

 The collection, though lacking many of the forms described in the 

 work under review, yet contains many species not represented in 

 the American collection. Considering, too, how well the British 

 forms are represented, including as they do Toulmin Smith's types 

 as well as those of the numerous species described by the late 

 Dr. Hinde, the student of Cretaceous Sponges has all the material 

 in the British Museum for ground-work, as well as for extended 

 research, and armed with Dr. Marjorie O'Connell's handbook 

 should be better equipped for this study than is the student of many 

 another invertebrate group for his special task. 



It may be gathered from what has been written how valuable 

 a book Dr. O'Connell has produced — one which in its thorough 

 treatment puts the new-comer at his ease by showing him exactly 

 where he stands in relation to his subject. Such a work should be 

 a stimulus to writers on other invertebrate groups and challenges 

 imitation. 



W. D. Lang. 



A Report on Magnetic Disturbances in Northamptonshire 

 AND Leicestershire and their Relations to the Geological 

 Structure. By Arthur Hubert Cox, M.Sc, Ph.D., F.G.S. 

 Phil. Trans. Roy. Soc. (A), vol. 219, pp. 73-135. 



T^HIS paper is published as an appendix to the Magnetic Re-survey 

 -*- of the British Isles for the epoch January 1, 1915, by Mr. G. W. 

 Walker. The earlier surveys of Rucker and Thorpe had revealed 

 the existence of sundry areas of special disturbance, not evidently 

 related to anything in the known geological constitution, and these 

 disturbances are confirmed by the new survey. To elucidate- their 

 probable cause two areas were selected for more comprehensive 



