146 



NATURE 



[June 18, 190S 



In his Introduction the author discusses some 

 questions of more general interest. After having 

 devoted a chapter to the classification of fishes, with 

 special reference to the Central American families, ex- 

 plaining the grounds on which he differs from some 

 of the generalisations proposed in recent years, he 

 proceeds to summarise the conclusions at which he 

 has arrived with regard to the geographical distribu- 

 tion of the fresh-water fishes. He begins with a 

 description of the range of the ten Central American 

 families and of many of their genera, tracing their 

 origin and migrations. Thus he says of the Cichlidae 

 {alias Chromides) : — 



" The Mexican and Central American Cichlidae are 

 more specialised than the South American ones, and 

 have certainly been derived from them ; not one of the 

 genera with three anal spines is found north of the 

 Isthmus of Panama, and all the South American 

 Cichlidae have simple conical teeth." 



He rejects the hypothesis of a nortlicrn origin of 

 Cichlidae and of their southward migration into South 

 America, Africa, and Southern India, and adopts the 

 view expressed by other zoologists that 



" In early Eocene times Africa was connected by 

 land with South .\merica on the one side, and with 

 India, via Madagascar, on the other." 



On the other hand, he takes the Cyprinodontidas to 

 be an originally Holarctic group, which, moreover, 

 was confined primarily to fresh water. His principal 

 reasons for the latter assumption are : — (i) their 

 absence from the Australian region, except for a species 

 of Haplochilus in Celebes and Lombok ' ; and (2) the 

 fact that all fossil Cyprinodonts known are from fresh- 

 water or estuarine deposits. .Singularly enough, while 

 in the old world all the species retained their ovipar- 

 ous habit, a very large number of the .American forms 

 became viviparous ; and it is in Central .'\merica that 

 some of the most specialised genera were developed 

 within comparatively limited districts. .Anableps is 

 considered to be endemic to South .'\merica, one Cen- 

 tral American species being an immigrant from the 

 South. 



The Centrarchid^ are also a northern tvpe which is 

 making its way southwards into Central America. Of 

 about thirty species, six extend southwards to the Rio 

 Grande, and one a little further into Tamaulipas. We 

 are glad to see that the author vindicates the North 

 American integrity of this group from the attempt to 

 associate with it the Indo-Pacific Kuhlia and its .Aus- 

 tralian fresh-water allies. 



These brief extracts will suffice to direct attention 

 to the many very interesting points on which the 

 author's thorough acquaintance with the subject en- 

 ables him to speak with authority. Several woodcuts 

 accompany the text, illustrating the distribution of the 

 Central .American families over the globe ; and on two 

 plates the northern range of Neotropical and the 

 southern range of Nearctic families and subfamilies 

 are shown. 



In the division of the Central American sub- 



' Prof. Max Weber could hardly allow even this exception, having incon- 

 testably proved that the scanty fresh-water fauna of Celebes is merely an 

 immigration from India. 



NO. 2016, VOL. 78] 



region into provinces, the author does not carry us on 

 firmer ground than had been reached by previous 

 inquiries. However, he expresses it as his opinion that 



" for fresh-water fishes the volcanic chain ot moun- 

 tains which stretches across Mexico from Colima nearlv 

 to Vera Cruz may be taken as the boundary between 

 the .Arctic and Tropical regions. This range has proved 

 an insuperable obstacle to the northward migration of 

 the Neotropical fishes." 



Having thus established a northern and southern 

 division, he distinguishes in the former three provinces, 

 viz. : — 



(i) Northern Mexico, west of the Sierra Madre. 



(2) Rio Grande province. 



(3) The Lerma system. j 

 .And in the latter : — 



(i) The Rio Balsas system. 



(2) Rio San Juan, with lakes Managua and 

 Nicaragua. 



(3) Guatemalan province. 



(4) Isthmian province (Costa Rica and Panama). 

 The author cautiously adds that any division into 



provinces must be regarded at present as merelv pro- 

 visional, owing to our incomplete knowledge of the 

 fish fauna of this area. \\"e cannot help thinking 

 that he would have much facilitated the labours of 

 future inquirers had he followed the plan of other 

 contributors and given a systematic index of species 

 with a table showing their range so far as at present 

 known. 



Finally, in the last chapter of the introduction the 

 author explains his views as regards the partial 

 identity of the fish faunas of the two sides of the 

 isthmus. He adopts the opinion of American ichthy- 

 ologists that there are very few of the truly marine 

 forms the representatives of which on the two sides 

 cannot be shown to differ in some point ; but on the 

 present occasion he takes into consideration such only 

 of the shore fishes as are known to enter fresh water. 

 He has prepared a list of eighteen pairs of such fishes, 

 each pair consisting of an .Atlantic and a Pacific 

 representative. The members of each pair differ from 

 each other in various degrees; some of them differ 

 in three or more "tangible," " substantive " 

 characters (and no systematic ichthyologist would 

 deny them specific rank), while others can scarcely 

 be regarded "as more than subspecifically distinct." 

 Thus, whatever method is followed by ichthyologists 

 for taxonomic distinction, with the object of accen- 

 tuating either the amount of differentiation that has 

 taken place since the individuals were separated and 

 isolated, or their previous and still more or less 

 apparent identity, the similarity between species of 

 both sides must be admitted by all to be so great as 

 only to be explicable by a former communication be- 

 tween the two oceans. 



The work is illustrated by twenty-six lithographic 

 plates executed by Mr. J. Green in his usual excellent 

 style, and we have to express our hearty thanks to 

 Mr. Tate Regan for having contributed so careful and 

 important a work to Godman and Salvin's great 

 undertaking. 



