No. 387.] DESMOGNATHUS FUSCA. 235 
into the dark lateral line which in time becomes lost in the 
dark color of the flanks, the result being similar to that seen in 
the lighter specimens of D. fusca. The ventral side furnishes 
a surer test, as it is usually of a light lemon yellow color in 
S. bilineatus and white and semi-transparent in D. fusca. 
This yellow color of the former species changes to a light 
-salmon pink in specimens thrown alive into aqueous corrosive 
sublimate. As for general shape and size, D. fusca attains a 
greater size, and in these large specimens (10 cm. +) the. large 
muscles of the jaw form definite protuberances upon the head. 
S. bilineatus is not as robust a species as the other, and the 
tail particularly seems more slender and longer in proportion. 
The number of costal folds may often be useful as a diagnostic, 
but this character seems liable to individual variation, and one 
is always in doubt where to place the beginning and end of the 
series counted. In D. fusca there are generally twelve folds 
(i.e. the myotomes, not the myocommata) between the fore and 
hind limb, while S. bilineatus shows usually fourteen or fifteen. 
These numbers can, however, be used for comparison only in a 
general way, for the relative position between these folds and 
the place of origin for the limbs appears to be subject to varia- 
tion. Perhaps the surest method of distinguishing is to collect 
a few typical specimens of each, and use them as standards for 
comparison, employing the other diagnostic points as they may 
seem applicable in individual cases. 
Eggs. —The eggs of S. bilineatus appear to be the more 
common, or at least the more usually found, and may be ob- 
tained during May and June. I have found them at the fol- 
lowing dates: May 27, June 12. They are deposited in a 
single layer upon the lower side of submerged stones, each 
batch containing from 30-50 eggs. The stones which are 
suitable for this purpose must be in the form of an arch allow- 
ing the water to flow beneath, as in the diagram, Fig. 1. They 
are generally in the more rapidly flowing portions of the brook, 
but the depth of water must be such that the eggs are at all 
times entirely submerged, as the dash of the surface ripples 
striking against them would subject them to mechanical 
injury. 
