70 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



Giiuther refers to the tendency to variation in these characters in the 

 common European sturgeon. 



Dumeril refers to the shorteuing of the snout and wearing away of the 

 ■plates, but is not influenced by his knowledge of the fact in establish- 

 ing species. 



Among many hundreds of sturgeon of different sizes brought in from the 

 nets and landed while we were visiting the fisheries of Lakes Michigan, 

 Superior, Huron, and Erie, not a single specimen was seen, of a size of 

 three feet or less, in which the five rows of shiekls were not developed 

 and keeled ; and if the young of the larger individuals are not represented 

 in these, they are not taken by the seines, pound-nets, or gill-nets that 

 gather in fishes from all parts of the lakes and streams. 



Up to an average length of about twenty-five inches the shields in- 

 crease somewhat in size ; afterwards there is a gradual diminution by 

 the wear of the keels and the absorption of the shield at the edges and 

 base. The snout, too, from the thin, elongated point of the smaller in- 

 dividuals, is dwarfed into the short, obtuse anterior extremity of the lar- 

 ger ones. 



Besides the examination of a large number at the fisheries with the ob- 

 ject of determining the number of species, we have made a minute ex- 

 amination of twelve specimens, of from one foot three inches to five feet 

 seven inches in length, from the lakes, with the following results : In 

 specimens of fifteen inches and less in length the shields are distinct, 

 large in proportion to the size of the fish, but crowded and imbricated j 

 up to about twenty-five inches in length-the shields increase somewhat 

 in size and become less crowded. The shields of these smaller speci- 

 mens have well-developed keels, terminating in a hook or spur, with a 

 sharp point. In those a little larger the points are found dull and the 

 hook disappearing. The keel, finally, is no longer apparent, leaving the 

 white, worn mark of its base on the shields. The shields decrease in 

 size from the edges ; those just anterior to the ventrals are the first 

 found missing ; the ventral shields disappear entirely, and the posterior 

 dorsal shields are next found missing, until a few of the anterior ones 

 are barely distinguishable ; even the callosities of the skin, showing the 

 former position of the shields, become effaced, so that it is impossible to 

 count the number of ventral or dorsal shields. The lateral series are the 

 most persistent, and have never been found in our observation entirely 

 effaced. In a description of a specimen from Lake Erie, Dumeril gives 

 the absence of the lateral shields as one of the characters. [Hist. Nat. 

 Poiss., p. 151.] 



This entire disappearance of the ventral shields is almost without 

 exception in the full-grown specimens. Examination of hundreds of spe- 

 cimens at the fisheries of the Detroit Eiver, at Sandusky, Ohio, where 

 a very large quantity are taken, at Waukegan, 111., Calumet, 111., and 

 the Lake Huron and Lake Superior fisheries, proved this fact beyond 

 question, the only exceptions being the retention of a remnant of the 



