24: MR. C. TATE REGAN ON THE 



is developed, can readily be found, although few cases are so 

 striking as the Phallostethinfe. 



Among fishes, one may lecall the curious Cyprinid Gyrinochilus 

 (Regan, 9, p. 29), which has the form, fins, scales, etc., of Crosso- 

 chilus and Discognathus, to which it is certainly closely related, 

 yet it has the mouth, gills, and pharyngeals so modified in con- 

 nection with its peculiar methods of breathing and feeding that 

 some ichthyologists have regarded it as the type of a separate 

 family. 



Because Neostethus and Phcdlostethus so obviously belong to the 

 large and varied family Cypi-inodontidie, one attaches but little 

 classificatory importance to the development of the priapium and 

 its evolution along two very distinct lines. But if these were the 

 only known Cyprinodonts they would certainly form a separate 

 order, and the differences in structure of the priapia would be 

 regarded not merely as generic, but as subordinal, and the much 

 longer anal fin, the abdominal groove, etc., of Phcdlostethus would 

 be held to support the view derived from the structure of the 

 priapia that it and Neostethus had diverged widely and through 

 a long period of time from their common ancestor. 



"Were these the only living Teleosts manjj" zoologists would 

 regard them as a separate class, comprising two well-marked 

 ■orders, just as some have suggested that the Dipnoans should be 

 removed from the Pisces, mainly on account of the isolated 

 position of their living representatives, Cer«ioc/!^ts and the Lepido- 

 .sirenidae, and have given these ordinal rank with the names 

 Monopneumones and Dipneumones. 



These somewhat fanciful considerations are put forward merely 

 to suggest that the rank given to a group depends on several 

 factors, and that the degree of diflferentiation is one of the least 

 of these. 



1 1 . Note on the Origin and Homologies of Skeletal Elements. 



The priapium appears to be an entirely new oi'gan, and it has 

 i\ highly developed skeleton, compi'ising a number of new ele- 

 ments that cannot be homologized with any pai'ts of the skeleton 

 ■of other fishes ; this suggests that the intermuscular connective- 

 tissvie may give rise to cartilaginous or bony elements whenever 

 and wherever the necessity may arise. This is, of course, not 

 new, but it is a point of view not always kept in mind by mor- 

 phologists, as could be illustrated by numerous examples, one of 

 which may be adduced. 



In certain Selachians, and especially in the Hypotremata, there 

 is a median series of vertical cartilaginous plates above the verte- 

 bral column, and the question has been raised whether these 

 belong to the vertebral column or to the fin-skeleton. Thus 

 ■Goodrich (Lankester's ' Treatise of Zoology,' pt. ix. figs. 50, 52) 

 has figured them in Squalus and SqiuUina, and has described 

 them as either modified radials or neural spines. I have long- 

 thought it probable that they were neither, but autogenous 



