74 PROCEEDINGS OF THE AMERICAN ACADEMY 



above, shows the sucking-disks reduced to a couple of rows of inde- 

 pendent suckers, but the young Lepidosteus no longer attach them- 

 selves by it. They have assumed the habits of the adult, rising 

 slowly near the surface, where they frequently remain almost motion- 

 less for a long time, merely keeping the pectorals and the tip of the 

 tail in rapid vibration. When they wish to swim about, they strike 

 out vigorously with their tail-fin laterally. 



When in a natural attitude, they float with the body curved, the 

 back behind the head flush with the surface, the head nearly hori- 

 zontal, and the tail curved down (Plate IV. fig. 39, Plate V.). 



By the 22d of June, the anterior part of the head had elongated, 

 and the indentations of the embryonic fin-fold marking the future fins 

 are deeper ; but the embryonic caudal is still by far the more promi- 

 nent of the two caudals, although the fin-rays of the permanent caudal 

 are well laid out, and its position has become more terminal than in 

 previous stages (Plate IV. fig. 38). 



The external changes undergone by the young Lepidosteus, until 

 the last one of them hatched at Cambridge died, were limited, in 

 the anterior part of the body, to the gi - eater elongation of the jaws ; the 

 increase in size and number of the teeth (Plate IV. fig. 41) ; 

 the growth of ventrals, which resemble in their structure that of the 

 pectorals (Plate IV. fig. 41a); and, in the posterior part of the body, 

 to the better definition of the shape and position of the dorsal, anal, 

 and caudal, as well as the great apparent increase in the length of the 

 temporary caudal filament, from the gradual resorption of the poste- 

 rior embryonic fin-fold. The head of the young Lepidosteus now 

 shows no further trace of the sucking-disk beyond the fleshy swollen 

 termination of the upper jaw. 



There are in this stage five gill-arches carrying short lateral 

 branches (Plate IV. fig. 43). Seen from below, the gill-covers 

 unite on the median line, immediately at the base of the lower jaw. 



The largest specimen grew to a length of \§ of an inch, and its 

 coloring (Plate V.) did not differ from that of larger young specimens 

 denoted by Professor Agassiz, which had already attained a length of 

 eight inches. 



In conclusion, we may say, as a result of the above observations on 

 the external development of the Lepidosteus, that, notwithstanding its 

 similarity to Sturgeons in certain stages of its growth, notwithstanding 

 its affinity with Sharks and Skates, by the formation of the pectorals 

 from a lateral fold, as well as by the mode of growth of the gill- 

 opening and the gill-arches, the Lepidosteus i3, spite of all this, not 



