PROF. ALEXANDER PUTRUNKEVITCH, a distinguished arachnologist, has furnished an account of the Pakæozoic Arachnida in the Transactions of the Connecticut Academy of Arts and Sciences, vol. 37, 1949 (New Haven.Conn., pp. 257, 7.70 dollars). This is particularly interesting in Great Britain, since it is very largely based on the rich collection of material in the British Museum (Natural History). lt is not simply a description of species, although 169 species are dealt with, but rather a review of their structure, classification and relationships. In order to carry out this work adequately, full cognizance is taken of the considerable advances made in recent years in our knowledge of the comparative anatomy and development of living forms. The description of the structure of both fossil and living Arachnida in general, the adequate definitions of the orders and the keys for their separation are useful not only to the palæontologist but also to the student of recent forms. The author concludes that at an early geological age the Arachnida split into a number of orders ; but that all of them exhibit the same fundamental trends, including a shortening of the abdomen through a loss of posterior segments. There is also a tendency to simplification, exemplified, inter alia, by the loss of abdominal appendages save the combs in scorpions, and the spinnerets in spiders, and, further, in the former by a reduction of the number of teeth in the comb and in the latter by a reduction of the number of spinnerets from four pairs to one pair. The work concludes with an interesting and useful discussion of these and similar trends, not only in the class as a whole, but also in its various subdivisions, and consideration of the evolutionary and classification significance of such trends. The paper is provided with a full bibliography, well indexed, and illustrated by eighty-three plates, thirty of which are excellent photographic reproductions of the material.