912 



SCIENCE. 



[N. S. Vol. III. No. 78. 



considerable degree appreciated twenty- 

 years ago. The reviewer, in the article 

 ' Ichthyology ' in Johnson's Universal Cy- 

 clopEedia (II., 1876) then gave the following 

 arrangement of the extinct types : 



' Super-order Dipnoi. 

 ' Order Sirenoidei. . 

 ' (?) Order Placoganoidei * (extinct). 



' Super-order (?) Aspidoganoidei (ex- 

 tinct) . 



'Order Cephalasiiidoidea (extinct).' 



The ' Elasmobranchs ' of Dean and Chi- 

 misroids have been segregated in another 

 class named Selachians or Elasmobranchs, 

 and the two main groups have been regar- 

 ded as sub-classes— Plagiostomes and Ho- 

 locephals. 



The Dipnoans and the Teleostomes are 

 scarcely separable as classes, although often 

 kept apart as such. The Dipnoans and 

 Crossopterygians lose some of their salient 

 characters, as we follow them back in time, 

 and have evidently^ diverged from a com- 

 mon stock. For the united group the class 

 name Pisces, or Teleostomi, can be used. 



Such are the opinions of the reviewer, but 

 perhaps Dr. Dean acted wisely in accepting 

 the classification adopted. The succeeding 

 pages teem with statements challenging at- 

 tention and often perhaps dissent. In al- 

 most all cases, however, weighty evidence 

 could be urged in favor of the views 

 adopted. There are few cases where we 

 feel disposed to bring forward objections, 

 but a comparison of ideas on some mooted 

 questions may be of interest and use. 



The ' explanatory tables ' towards the 

 end of the volume give facts respect- 

 ing the ' skeletons of fishes ' (pp. 252, 

 253), 'relations of the jaws and branchial 

 arches of fishes' (pp. 256, 257), ' the heart 

 of fishes' (260), ' a comparison of gills, 

 spiracle, gill-rakers and opercula ' (260, 

 261), 'digestive tract' (263), ' swim-blad- 



* Placoganoidei was ao ordinal name for the Plaeo- 

 dermi with dipuoan dentition. 



der' (264), 'genital system ' (266), 'cir- 

 culation of fishes' (269), 'excretory sys- 

 tem and urinogenital ducts' (270, 271), 

 ' abdominal pores' (271), 'the central ner- 

 vous sj^stem of fishes ' (274, 275), ' the 

 sense organs ' (276, 277), etc. 



These tables give a large amount of use- 

 ful and tolerably^ well digested information 

 illustrated by apt figures and arranged 

 under the main groups of fish-like verte- 

 brates, as Cj'clostomes, Sharks, Chimter- 

 oids. Lung-fishes, Ganoids and Teleosts. 

 But useful as the tables are, the ordinary 

 reader will be liable to fall often into error 

 if he allows himself to trust them too im- 

 plicitly. The exceptions to the general 

 propositions are very numerous. Examples 

 of such are ' tail heterocercal ' (p. 252) in 

 Selachians, or ' Sharks ' and Rays, ' oper- 

 culum, pre-, sub- and inter-opercula,' in Tel- 

 eosts, etc. (261), 'many pyloric cseea ' in 

 Teleosts (263), and air bladder in Teleosts 

 as in Sturgeon (264) but ' may be absent 

 (Pleuronectids).' Hosts of the fishes re- 

 specting which the characters in question 

 are predicated differ from the majority in 

 wanting them. The remarkably aberrant 

 Lyomeres, indeed, want all. 



The anatomical portion is generally satis- 

 factory', so far as it goes, and, although we 

 may sometimes differ from the author as to 

 homologies, he seldom falls into absolute 

 error, as he does, for example, in calling 

 the ventral fins of Ophidium ' barbels ' (p. 

 47). He may be congratulated on having 

 divested himself of ' his former view that 

 the pineal foramen of Dinichthys contained 

 a specialized optic capsule ' (55) and of a 

 corresponding view respecting the ' pineal 

 foramen ' of Siluroids. Apropos of the Silu- 

 roids, we feel disposed to dissent from Dr. 

 Dean's statement respecting ' the most com- 

 plete encasement of a fish's bodj' dermal 

 plates ' as manifest in callichthyids. He 

 thiulis that the two lateral rows of plates 

 are the result of ' extended fusions, a single 



