128 Reviews — Nicholson and Lydekker's Palaeontology. 



met with in each division of the Invertebrata are not merely de- 

 scribed but well illustrated, not a single figure is devoted to the 

 histology of the Vertebrata, and there are no descriptions of tissues 

 that can be regarded as precise or in all respects accurate. Again, 

 the excellent plan of printing in italics concise definitions of each of 

 the great groups, adopted throughout the first volume, is not followed 

 in the second ; and the insertion among the figures of Vertebrata 

 of several woodcuts, whose only interest consists in their antiquity, 

 and of which the accuracy is in inverse proportion to their age, 

 forms a striking contrast to the selection of figures employed for the 

 illustration of the Invertebrata. 



A brief general statement of the principal characters of the Verte- 

 brate skeleton follows the definition of the sub-kingdom ; and each 

 class is subsequently treated in more detail at the head of the section 

 relating to its extinct representatives. 



In the general description of the Class Pisces, the absence of any 

 precise description of the histology of the exoskeleton is especially 

 unfortunate ; and even more so is the allusion to Selachian dermal 

 tubercles as " bony " and " supported on bone." One of the more 

 frequent problems to be solved by the Pala^iobthyologist has refer- 

 ence to the true nature of detached fragments of the dermal armour 

 of fishes ; and the differences between (i) the vascular dentinal 

 structure characteristic of Elasmobranchii and Cbimasroidei, (ii) the 

 isopedin of some of the earlier " Ganoids," and (iii) the true bone of 

 Sturgeons and other " Ganoids," are so distinct and noteworthy, that 

 the most elementary guide to the student ought to provide detailed 

 descriptions with figures. The illustrations of cycloid and ctenoid 

 scales (figs. 832, 833) will also prove somewhat confusing ; the 

 smooth posterior border being directed downwards in the first, and 

 the prickly homologous border turned upwards in the second. The 

 statement that there are no neural and hasmal arches in the vertebral 

 column of Sharks (p. 915) is rightly contradicted by descriptions 

 and figures in the following chapter ; and the brief allusion to the 

 " pelvis " on p. 919 is scarcely so explicit as desirable. The earliest 

 known fishes are not Placodermata (as stated), but Pteraspidians ; 

 and, following the latest researches, the author dismisses conodonts 

 with a brief mention, illustrated by the familiar figure. The classi- 

 fication pix>posed by Huxley, in 1876, is adopted, each of the six 

 divisions being termed orders, and all except the first (Cyclostonr.) 

 having undoubted extinct representatives. 



The Elasmobranchii are treated for the most part in accordance 

 with the British Museum Catalogue ; and the singular family of 

 Squaloraiidaa is placed in the Chimasroidei on the authority of Dr. 

 Traquair. The Dipnoi comprise the Lepidosirenidaa, Ceratodontidas, 

 Phaneropleuridaa, and Dipteridas ; and the Ganoidei follow, arranged 

 and subdivided as suggested by Dr. Traquair. Here, unfortunately, 

 some minor inaccuracies occur, and the selection of several of the 

 woodcuts is far from satisfactory. The canals of the " lateral line," 

 for instance, have only been found in the Pteraspidae, not in the 

 Cephalaspidse ; there are no Lower Devonian rocks in " North 



