6 MONOGRAPH OF THE FRESH WATER III. 
In our Revision of the genus Cottus,: we advanced the opinion that this species 
would be found distinct, not knowing at that time that it had been already named. 
These were progressive steps in European ichthyology, but there still remains 
carefully to compare with the above species, the C. gobio of England, France, Den- 
mark, Germany, and Russia, in order to ascertain whether several species are not 
still confounded. We have already remarked a certain disagreement on this subject 
among authors. Cuvier makes the positive remark that the C. gobio has only three 
soft rays to the ventral fins, whilst Dr. Richardson mentions four as belonging to 
the English species examined by him, and which is the same as the one described 
by Mr. Yarrell. This also has but six spinous rays to the first dorsal, and sixteen 
soft and articulated, but unbranched rays, to the second dorsal. The assertion 
of Cuvier, that the first dorsal of C. gobio counts from six to nine spinous rays, is 
a fact to be verified anew: perhaps the above English species is taken into account 
in the formula. Moreover, Cuvier says, positively, that the rays of the centre of 
the second dorsal dichotomize at their extremity. Finally, in the C. gobio of the 
Seine the upper rays of the pectorals are branched, whilst they are all simple in 
the English species spoken of by Dr. Richardson. 
Should these differences prove constant, and we have no doubt they will, they are 
more than sufficient for specific distinction, and we are satisfied of the existence of 
two species of Cottus in the British Islands, for we find mentioned sometimes three 
and sometimes four rays to the ventrals of the so-called C. gobio. This character, 
which proves safe among American species, will no doubt be a sure guide in a 
critical review of the European ones. We have seen a mutilated specimen of an 
English Miller’s Thumb with evidently branched pectoral rays, therefore differing 
from the one alluded to by Sir John Richardson. The Miller's Thumb from the 
Seine again differs from that of the Danube. Those of the Rhine, of the Rhone, 
and the south of France generally, deserve a special attention, as well as the one 
mentioned by Reisinger in his /chthyologicee Hungarie, which seems to attain a very 
large size. In fact, the Cottoids of all the European and Asiatic rivers and lakes 
should be compared directly. It is only after this is done that we shall be prepared 
to establish safe comparisons between the species of one continent and another. 
Now, if we recapitulate the European species, we find five of them to be well 
determined and named. In addition, we have two species in England as alluded 
to above, which are distinct from C. gobio of the Seine; thus giving seven species. 
Then, in central Europe several other species will probably be found distinct. 
C. peecilopus must be compared with the gobio of Reisinger, of the Danube. Be it 
remembered that the latter spawns in March and April. A comparison of the 
C. gobio from the Seine (spawning in May, June, and July) with that of the south 
of France, and then again with that of the Swiss lakes and the rivers of conti- 
nental Europe, would no doubt add to the number of species. It would be inte- 
resting to know whether the Miller’s Thumbs exist southwards of the Pyrenees, 
in Spain and Portugal, as well as in Greece and Asia Minor. 
+ Nouveaux Mémoires de la Société Helvétique des Sciences Naturelles, vol. xii., 1851. 
