ASTACID^E. 13 



areola vertebralis affords the best characteristic marks. I have never 

 known this last character to vary in any degree. In the two others 

 there may occur slight differences of development, not, however, so 

 great as to be of any moment." According to these remarks, Dr. J. Le 

 Conte seems to be convinced that the size of the areola vertebralis is 

 alone constant and always identical, and thus confirms the result of the 

 labor undertaken some years afterward for the European species by Mr. 

 Gerstfeldt. I have to add that Mr. Gerstfeldt does not speak at all of 

 the areola vertebralis, because it is not so well marked in the true 

 Astacus, and that Mr. Gerstfeldt also has proved all the other charac- 

 ters to be variable in some degree. I am obliged to go a little further, 

 and to state that, according to my observations, even the areola verte- 

 bralis varies to a greater or less extent. 



Abnormal Gigantic Specimens. — It is very necessary to give up the idea 

 that specific characters should bear a mathematical identity. Crustacea, 

 as is well known, grow continually, and possibly become very old. 

 Therefore we sometimes find of a species, which commonly has certain 

 and smaller dimensions, some old and gigantic individuals, differing in 

 many characters (viz. in sculpture, armature, relative size of parts and 

 members) from the common examples of the same species. As pro- 

 gress is made in the cultivation of the land, and the improvement of 

 the rivers, and especially as the population of the country increases, 

 these giants become more and more rare in the species used as food, as 

 in A. fluviatilis of Europe. Perhaps the extraordinary dimensions given 

 by Eafinesque fifty years ago — for A. limosus nine inches, for A. fossor 

 six inches, while at this time the specimens, seen by me are only half as 

 large — are explicable in this way. I remark, however, that the Amer- 

 ican species are not commonly used as food, except by the French pop- 

 ulation of the Southern States. 



But even aside from these abnormal instances, other younger and 

 older specimens present quite a variable material for comparison and 

 description. If you state, for instance, that the specific characters 

 should be only taken from the full-grown specimens, this statement is not 

 at all decisive, because it is impossible to determine whether a specimen 

 be full grown or not. In Norway it is against the law to sell lobsters 

 not full grown ; and the law considers every lobster over eight inches 

 long as full grown, because it is supposed to have spawned three times. 

 But the lobster may become twice that size ; it would then differ in 

 sculpture, armature, and the relative size of its members, as mentioned 

 before. The real difference is far greater, as it is reasonable to con- 

 sider every lobster after its first spawn, although then much smaller, 

 as a full-grown animal. 



Although a good and complete description of a species should enable 

 us to determine both the young and the full-grown specimens, still the 



