CHAPTER VII. 



GENERAL CONSIDERATIONS. 



A number of interesting and important facts, bearing on general biological 

 problems, are incidentally dealt with in the systematic portion of this paper. 

 Inasmuch as it is not at all to be expected that anyone would read through the 

 mass of details to discover them they are extracted and presented here. 



"Unnatural Natural History." 



The skeletons of a variety of the Ariince are prepared and sold as "crucifix 

 fishes." The one which is most frequently prepared is Sciadeichthys proops (Plate 

 VI) . The dorsal surface of the skull and dorsal plate are pointed out as resembling 

 a hooded monk with outstretched arms. The ventral surface resembles the 

 cross. Fancy pictures the dorsal spine as a representation of a spear, while the 

 otoliths, which rattle when the skull is shaken, are the dice with which the 

 soldiers cast lots for the garment of our Lord. 



Skulls of the Aspredinince are put together to form a "crown of thorns." 



Jordan's Law. 



If we should find specimens of any group with such slight differences as there 

 are between Crenicichla saxatilis and alta or Mquidens vittatus and potaroensis 

 generally present at any locality we should probably consider them as variations 

 without special significance. The differences must, however, be of distinct sig- 

 nificance, if they are coordinated with the environment in such a way that one can 

 predict what the form will be at any locality. 



In the present paper such forms have been given specific designation. Thus 

 Mquidens vittatus of the lowlands is replaced by Mquidens potaroensis in the Potaro 

 River, both above and below the Kaieteur. Similarly Crenicichla alta replaces 

 Crenicichla saxatilis, the two forms overlapping at Rockstone. Similar replace- 

 ments of lowland species by highland species are abundant. Rhamdia quelen of 

 the upper Potaro replaces Rhamdia sebas of the lowland. Hehgenes marmoratus 

 replaces Hypophthalmus edentatus. Plecostomus hemiurus replaces Plecostomus 



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