xlv 



ferences exist among the constituents, they are overshadowed by the 

 I closer agreement as compared with other groups, and the tendency, 

 therefore, is to depreciate their value. The Nematognathi is a case in 

 point. The ordinal or even subordinal value of the group has been 

 admitted by few, and generally it is considered as a member of the " order 

 Physostomi," and as it is really a natural and homogeneous group and 

 strongly contrasts with any other, by many it has been endowed with only 

 family rank. Yet the internal and external differences existing within 

 its limits are very great, and really as obvious and by every analogy as 

 important as those which the mind has become habituated to consider as 

 of family value in other cases. And furthermore, the anatomical charac- 

 ters differentiating the group from others are many, striking, and, as shown 

 by the extent of variation within other groups, very important. The 

 exigencies of classification, therefore, seem to demand in such a case 

 ordinal distinction, and then the constituents of the group naturally resolve 

 themselves into sections whose importance, not being weighed in bulk 

 against another family, can be appreciated, and the mind is prepared to 

 admit their superior value. 



ACKNOWLEDGMENTS, ETC. 



Among those recent works mentioned in the bibliography or incidentally 

 in the introduction, he has been especially benefited by the memoir of 

 Prof. Cope, so often referred to. If he has sometimes found reason to 

 express dissent from that eminent naturalist, it is because the importance 

 of the memoir in question and the extensive knowledge of its author, have 

 induced him to review and weigh the evidence affecting the questions in 

 dispute. And the superior ability and learning of Prof. Cope appeared 

 to demand reasons for any dissent from his views. 



In order to enhance the usefulness of the catalogue, references are made 

 to Dr. Giinther's " Catalogue of Fishes in the British Museum," that being 

 emphatically the vade-mecum for the working ichthyologist, and necessary 

 to be constantly referred to for identifications, verifications, or references. 

 In addition, in some cases, references are made to other publications, and 

 when the names repeated from such authorities are not recognized by or 

 are different from those employed by Dr. Giinther, or when they accompany 

 different groups, the reference to Giinther's work is generally abbreviated 

 and inclosed in parentheses after the primary reference, thus, " (G. iii., 200 

 -205)." 



Specific acknowledgment is due to the greatest of Spanish naturalists, 

 Prof. Poey, of Havannah, Cuba, for his courteous attentions for many 

 years, especially manifested in the transmission, for my use, of the fishes of 

 Cuba, including many of the types of his new species 5 I am also iirdebted 



