Geology and Mineralogy. 397 



peculiar group of organisms to those living and more familiar types 

 of structure, the reptiles, birds and mammals. Step by step the 

 peculiarities of the structure of the rare bones are compared 

 with known structures in other animals. The reconstructions 

 made become understood and real and reasonable; and the 

 reader, though unfamiliar at the outset with the technical names, 

 leaves the book with a new vocabulary which means something 

 real to him. While extremely skillful in picturing Lis own con- 

 ceptions of the animals represented by the fossils studied, the 

 author is also precise and scientifically accurate. Whatever criti- 

 cism may be made of his classifications or of the affinities assigned, 

 the reasons for them are definitely based upon the observed facts. 

 The Ornithosauria are traced for origin not directly to reptiles 

 or birds, as now known and defined, but rather to unknown 

 ancient stock, in which were combined rudimentary characters 

 which, by elimination of some and modification of others, have 

 resulted in the differentiations represented by the Reptilian, Bird, 

 Ornithosaurian and Mammalian types. 



"If we ask," the author writes, u what started the Ornitho- 

 saurian into existence, and created the plan of construction of 

 that animal type, I think science is justified in boldly affirming 

 that the initial cause can only be sought under the development 

 of patagial membranes such as have been seen in various animals 

 ministering to flight." But there was " no geological history of 

 the rapid or gradual development of the wing finger, and 

 although the wing membrane may be accepted as its cause of 

 existence, the wing finger is powerfully developed in the oldest 

 known Pterodactyles as in their latest representatives." " Ptero- 

 dactyles show singularly little variation in structure in their 

 geological history," and what there was has to do chiefly with 

 loss of characters early possessed or variations in size and parts. 



Regarding the affinities of the Ornithosaurs the author remarks, 

 "It would therefore appear from the vital community of struc- 

 tures with Birds, that Pterodactyles and Birds are two parallel 

 groups, which may be regarded as ancient divergent forks of the 

 same branch of animal life, which became distinguished from 

 each other by acquiring the different condition of skin, and the 

 structures which were developed in consequence of the bony 

 skeleton ministering to flight in different ways; and with dif- 

 ferent habit of terrestrial progression this extinct group of ani- 

 mals acquired some modifications of the skeleton which Birds 

 have not shown. There is nothing to suggest that Pterodactyles 

 are a branch from Birds, but their relation to Birds is much 

 closer, so far as the skeleton goes, than is their relation with the 

 flightless Dinosaurs, w 7 ith which Birds and Pterodactyles have 

 many characters in common." The book will prove as useful to 

 the paleontologist as to the general reader, for it furnishes a brief 

 but clear and systematically arranged compendium of the chief 

 facts known regarding this unique group of extinct animals. 



The illustrations are not the least important feature of the 



