^^^gg^!''] PROCEEDINGS OF THE NATIONAL MUSEUM. 9 



tire series of Mesozoic deposits from the Trias to tlie Cretaceous, inclu- 

 sive." Their distribution has evidently become limited in later times 

 and the living members may be looked upon as but remnants of an 

 older fauna. 



The number of species of the Symbrmichichv is also quite limited, 

 while their geographic range is very large, Nearly all such cases are 

 to be explained by a greater abundance and a wide distribution in 

 former times. The living species enter brackish water, while one genus 

 is strictly marine. Dr. Giinther says of this fish (Study of Fishes, 

 p. 226): "The occurrence and wide distribution in Tropical America 

 of a fish of the Indian family Symbranchtda', which is not only con- 

 generic with, but also most closely allied to, the Indian Symbranchus 

 bengalensis, offers one of those extraordinary anomalies in the distri- 

 bution of animals of which no satisfactory explanation can be given at 

 present." 



The present is evidently the age of the Nematognathi and the Even- 

 tognathi. Probably all the species of Xematognathi of South America 

 are autochthons of that continent. A pretty complete series still exists 

 without taking into account any species of other regions. The\' are 

 chiefly lower forms, although some of them have reached a high state 

 of specialization in a certain direction. Their evolution has already 

 been discussed by us in various places and it is not necessary to rei)eac 

 all the considerations here. 



The peculiarities of the Diplomystidce have been pointed out above. 

 We must conclude from the presence of dentiferous maxillaries and the 

 absence of all the barbels except the maxillary,* either that this family 

 represents the ancient Nematognathi, or that it is a reversion to the 

 ancient forms. The former conclusion seems preferable. Siluridce have 

 been found in the eocene Tertiary of Europe, while the Wasatch beds, 

 the lowest Tertiary of North America, have yielded several species 

 of a genus {Bhineastes) probably related to the Pimelodmce, from which 



* The value placed on the maxillaries can not be questioned, while the value placed 

 on the presence or absence of certain barbels is fully warranted both by the living 

 forms of South America and by the embryology of Ictalurus alMdiis (Le Sueur). Pro- 

 fessor Ryder (On the Development of Osseous Fishes, p. 49, Washington, 1886) says: 

 "The remarkably developed barbels of the embryos of this species make their ap- 

 pearance very early, especially the maxillary pair ; these appear on the second day. 

 * * * The barbels on the lower jaw do not appear till the fourth day of develop- 

 ment is completed. * * » The last of all to be developed is the nasal pair * * « 

 [which] doesnot appear until the seventh day." Page 54 : "Whether the endoskeletal 

 part of the upper end of the so-called maxillary barbel in reality represents the 

 maxillary bone of other fishes seems somewhat open to doubt, as the proximal ossi- 

 fication of the cartilaginous support of this barbel would give this element in the 

 catfishes a cartilaginous origin, which is at variance with what is known of the 

 development of its homologue in all other forms of Teleosts, in which it arises as a 

 membrane bone." At the time of writing this Professor Ryder was probably not 

 familiar with the peculiar Diplomystes. 



