Introduction. 



The mail-cheeked fishes, first grouped together by Cuvier and Valenciennes ('29), are said to 

 be all characterized bythe presence of a suborbital stay, that stay being formed by the extension across 

 the cheek, toward or to the operculum, of the third infraorbital bone. In other respects certain families 

 of the group differ greatly from the others, so much so that they have frequently, since Cuvier's time, 

 been widely separated in classificatory schemes. Modern tendency is however to bring the several 

 families together again, Boulenger ('04), the most recent writer on the snbject, placing them all in a 

 Single division of the Acanthopterygii, which he calls the Scleroparei. Preceding Boulenger, Gill ('88), 

 and, following him, Jordan and Everniann ("98), keep the several families of the group together, but 

 separate them into two suborders, the Loricati and the Craniomi. The latter fishes are said by these 

 authors to be derived from the former and to be distinguished from them, essentially, by the following 

 features only: 1. by the abnormal character of the scapular arch; 2. in that the post-temporal (supra- 

 scapular) forms an integral part of the cranium; and 3. that the postero-temporal (supraclavicular) 

 is .,crowded out of place by the side of the proscapula above or at the edge of the post-temporal". 



Of the numerous fishes of the group I have had specimens of the following species, and they 

 have all been more or less carefully examined in connection with the present work: 



Scorpaena scrofa, S. porcus, 



Sebastes dactylopterus, 



Cottus octodecimospinosus, C. scorpius, 



Trigla hirundo, T. gurnardus, T. lyra, T. pini, T. lineata, T. obscura, 



Lepidotrigla aspera, 



Peristedion cataphractum, and 



Dactylopterus volitans. 



The three specimens of Cottus octodecimospinosus and the two specimens of Trigla gurnardxis 

 that I have had, were kindly sent me, respectively, by the U. S. Fish Commission Station at Wood's 

 Holl, Mass., and by Dr. Allen of the Plymouth Biological Station, England. Of Cottus scorpius I have 

 had only a few embryos and larvae kindly sent me by Prof. W. C. Mc. Intosh of St. Andrews, Scot- 

 land. Of Dactylopterus vohtans one of the several specimens was obtained from the Naples Zoological 

 Station. The other specimens used in the investigation were all found in the market here (Menton) 

 or at Nice, and, although they are all Mediterranean species, I have not always been able to satisfac- 

 torily identify them; for the features given by Günther ('60) as of specific value are often very variable, 

 and there are apparently, in many of those features, an almost perfect series of intermediate types. 



