Post-Larval Stages. 13 



development. It is possible that tliis difference, and the fact that the smallest 

 specimen from the Mediterranean had already the complete number of rays in the 

 first dorsal fin, led Stiasny into error regarding the sequence in development of the 

 rays of the first dorsal fin. The 10-mm. long specimen, described by Fulton, from 

 the North Sea, had not yet developed the true first ray. In reality the first ray 

 is the last to make its appearance in the development of the first dorsal fin, and the 

 Scottish specimens do not reach this stage of development until they are about 

 15 mm. long. On the other hand, the Mediterranean forms, at a length of 15 mm., 

 show the separation of the first ray of the first dorsal fin into a long thin stalk and 

 a flap-like termination. 



Stiasny states that the first small teeth in the upper and lower jav/ are visible 

 in individuals of 17 mm. long. According to Fulton, the 10-mm. long form, 

 described by him, showed 10 to 12 small pointed teeth. In the present series, the 

 first indications of teeth on the jaws were made out in specimens with five dorsal 

 fin-rays. 



A post-larval form of about 30 mm. in length has been described by Agassiz 

 (1882), but here again Mediterranean specimens of a similar size are further 

 advanced in development than the American one. Agassiz' post-larval specimen, 

 although very much larger than the largest North Sea specimens, resembles these 

 much more closely than it resembles the Mediterranean ones. The description 

 given by Agassiz may, therefore, be used to bridge the gap between the oldest 

 post-larval form here described and the smallest bottom stage. 



" Although the body is still laterally compressed, the head, which has greatly 

 increased in size, as well as the body anterior to the anal opening, have become 

 somewhat flattened ventrally, the first trace of the great flattening so characteristic 

 of the genus. The anterior part of the head projects proportionally far in advance 

 of the orbits, the head sloning less from the base of the anterior dorsal ray than in 

 preceding stages. The pectorals have now become enormous ; they extend across 

 the whole width of the body of the young Lopkius ; they are lobed at the edge, 

 the rays articulated, well-marked, and edged with rows of elongated dark pigment 

 spots. The tail is well-formed, though it still retains its ganoid shape, and the 

 posterior dorsal and anal, though well-formed, are still connected by a distinct 

 remnant of the dorsal and ventral embryonic fin-fold with the caudal fin. The 

 anterior dorsal now has five rays, with a rudimentary one anterior to the first formed 

 ray. These rays are connected at the base by a fin-fold at a much higher point than 

 in younger stages ; they extend far beyond the fold ; the extremities curve down 

 about a quarter of the" length of the ray. The increase in length of the ventral 

 rays has been still more remarkable. The original ventral ray is nov/ nearly twice 

 as long as the body of the fish, and the second ray extends fully as far as the 

 extremity of the caudal fin. There are two shorter exterior rays and one interior 

 ray ; they are joined by a membrane extending nearly to the base of the caudal, 

 so that when expanded and seen from above the ventrals appear like regular wings." 



It is to be noted that, in the American specimen, the first ray of the first dorsal 

 fin is still small. Again, the membrane, which connects the posterior rays extends 

 high up the rays, whereas in vStiasny's forms this membrane does not extend beyond 

 the base of the rays. Further, although the second dorsal, anal, and caudal fins 

 are well formed, the embryonic fin-fold still persists. In Stiasny's series, the 

 embryonic fin-fold has dwindled considerably before this size is reached. 



If the above differences are kept in mind, the later stages described by Stiasny 

 may be considered briefly. In the young fish of 22 mm. length, the fan-shaped pelvic 

 fins have increased to almost twice the length of the body ; at a length of 27 mm. 

 the membrane connecting the rays has grown still broader so that they give to the 

 fins, especially in movement, the appearance of wings ; whilst, at 30 mm., the 

 thread-Kke prolongations of the rays are still very long, often twice as long as the 

 body, or more. In the Mediterranean specimens at a length of 17 mm., there is 

 the first sign of the little leaf -like appendages at the border of the under jaw. 

 These rugged tags increase in number on the whole body as the fish gets longer. 

 There is a general and gradual flattening of the head, and at the length of 50 mm. 

 the head has increased still further in size and has grown flatter, the breadth now 

 exceeding the height by 2 mm. Stiasny states that at this stage, apart from the 

 still thread-like appendages, the wing-like pelvic fins and the broad pectorals 



