268 NATURAL SCIENCE. April, 



"that the pineal structures of the true fishes do not tend to confirm 

 the theory that the epiphysis of the ancestral vertebrates was con- 

 nected with a median unpaired eye ; it would appear, on the other 

 hand, that both in their recent and fossil forms, the epiphysis was 

 connected in its median opening with the innervation of the sensory 

 canals of the head." 



The lampreys and their allies, as usual, are treated as a separate 

 class (Marsipobranchii) below the fishes, and form the subject of 

 chapter iii. The Devonian Palcrospondylus here takes its apparently 

 proper place ; while the curious Silurian and Devonian Ostracoderma 

 are also provisionally arranged in the same class. The figures of the 

 latter are not so well chosen as they might have been, but the text is 

 thoroughly up-to-date. 



The sub-classes of true fishes are treated in four successive chapters, 

 each arranged on the same plan. First are enumerated the principal 

 structural characters of the members of the sub-class, with at least 

 one figure of the soft parts and one of the skeleton. Next, the more 

 important extinct types are noticed, and then, similarly, the leading 

 surviving types. Finally, the probable affinities and interrelation- 

 ships of the sub-class are briefly tabulated, in two cases also graphi- 

 cally represented in a diagram. 



Among fossil sharks, the Devonian Cladoselache occupies the first 

 place as the most primitive, as also the oldest known, genus. As 

 Dr. Dean has proved elsewhere, it represents an otherwise unknown 

 order of Elasmobranchii. The Acanthodians are noticed next, with a 

 restoration of Acanthodes which has much too small an orbit. Then 

 follow the Pleuracanthidae, with a slightly modified copy of Dr. 

 Fritsch's restoration of Pleuracanthns decheni, and a very misleading 

 figure by Davis representing an absolutely indeterminable fossil, 

 though labelled " dermal bones of the head roof of Pleuracanthns.'' 

 After a few other remarks on extinct sharks, the brief enumeration ot 

 the principal types of existing elasmobranchs begins with Chlamy- 

 doselache and Notidamis, and ends with the rays, which Dr. Dean 

 thinks arose " in early Mesozoic time from the main shark 

 stem, not from Cestracionts, Pristids, Pristiophorids, or even (?) 

 Rhinids." He concludes that, " of all known stems, that of the 

 shark is most nearly ancestral in the line of jaw-bearing vertebrates." 



Chapter v., on Chimaeroids, is necessarily short, and chiefly 

 remarkable for the beautiful figures of the deep-sea genus Harviotta, 

 now first reproduced in a text-book. Fossil remains are also well 

 represented. 



The general characters of the Dipnoi are illustrated by a partial 

 modification of W. N. Parker's figure of the soft parts of Protopterns, 

 and by a beautiful new drawing of the skeleton of the same genus. 

 There are also new restorations of the Devonian genera Dipterns and 

 Phaneroplemon. The Devonian Arthrodira, or Coccosteiis-\\ke fishes, 

 are doubtfully placed at the end of the Dipnoan series, and Dr. 

 Dean's account of the American forms is of importance as being 

 based on personal observation. A series of drawings of the man- 

 dibular bone in several of these remarkable fishes is particularly 

 interesting, as also is the new photograph of the skull of Dinichthys 

 forming the frontispiece of the book. 



The account of the Teleostomi, or " ganoids " and " teleosteans," 

 is compressed within forty pages, and is thus extremely sketchy. All 

 the main features in the development of the group, however, appear 

 to be mentioned ; only those readers will be disappointed who seek 

 for a formal arrangement of this sub-class, which comprises the vast 



