[103] FLOUNDERS AND - SOLES. 327 



of the genus. If its scales are really keeled it may form the type of a 

 distinct genus. The increased number of fin-rays also indicates a 

 probability that the number of vertebrae will be found to be similarly 

 increased. For the subgenus of which this is the type, we have sug- 

 gested the name of Acedia. 



LARVAL FORMS. 



(BlBRONIJE.) 



The very young of all the Pleuronectidce so far as known are trans- 

 parent and with the eyes symmetrical. At a length of from one-fourth 

 of an inch to an inch the eye of one side moves by degrees to the other 

 side, where it becomes the upper eye. The question has been much 

 discussed as to how this change comes about — whether by a twisting 

 of the head so that the eye moves over the line of the profile, whether 

 by passing from side to side beneath the frontal bone, or by passing 

 between the frontal bone and the bases of the dorsal rays, or whether 

 by each of these methods in different genera. The present writers have 

 had no opportunity to make any observations on this point, the state- 

 ments which follow being entirely drawn from others, chiefly from the 

 papers of Dr. Luigi Facciola.* 



According to Prof. Japetus Steenstrup,t who has examined some 

 " plagusiiform" specimens (Symphurus?) about 25 millimeters in length, 

 the eye, by a combined movement of rotation and translation, goes from 

 its original position to the other side by passing under the frontal bone. 



In other flounders examined by Prof. Alexander Agassiz the eye 

 is said to have crossed from side to side above the frontal bone, pene- 

 trating the space between this bone and the dorsal fin by sinking into 

 the tissues of the head. In the species examined by Dr. Facciola the 

 eye was found to pass between the frontal bone and the dorsal rays, 

 but without penetrating any tissues. During the passage of the eye 

 the first dorsal ray formed a projection detached from the cranium, and 

 in the notch between this and the head the eye has passed from one side 

 to the other. 



It has not been easy to determine with certainty the species to which 

 these larval forms belong. The first of these which were known were 

 described by Cocco as distinct genera, allied to the flounders, but dis- 

 tinguished from them by the symmetrical arrangement of the eyes. 

 For the group thus defined Bonaparte has proposed the family name 

 of Bibronidi (Bibroniidcc), and this name has been adopted by some of 

 the Italian ichthyologists. 



* " Sulla StatoGiovanile del Iihomboidichthys mancus," Facciola, Natnralista Siciliano, 

 vi, 1887, and " Su di Alcuiii Rari Pleuronettidi del inare di Messina, " Nat. Sicil., iv, 

 1885. 



t "Om Skjsebheden hos Flynderne og navnlig oin Vandringen af det ovre Oie fra 

 Blindsiden til Ojesiden tvers igjennem Hovedet," 1864. * 



