4 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
breed in May and the sole about the end of June. I can find no ac- 
count of the breeding time of Limanda. P. americanus breeds from 
the middle of February to the first week of April. 
In the summer of 1899, when P. americanus was especially plenty, 
metamorphosed fish of two different lengths were taken in the tow. 
These were about equally abundant. The smaller measured not over 
8-9 mm. at the end of metamorphosis. The larger was a more bulky 
fish with slightly more pigment and it was found swimming upright 
until it reached a length of 13-14 mm., when it also turned left side 
down. I found no specimen intermediate between the two lengths. The 
larger, more pigmented specimens may have been either the larve of 
the black-bellied variety or possibly the young of Limanda. The more 
important specific differences between Limanda and Pseudopleuronectes 
are the following: The anterior part of the lateral line of Limanda is 
more arched and this species has more fin-rays in both dorsal and ventral 
fins. But it is difficult in the young fishes to establish a satisfactory 
division on the basis of the number of fin-rays. According to Bumpus 
(98), P. americanus at Wood’s Hole averages 66.1 fin-rays to the 
dorsal and 49.6 to the ventral fin. Jordan and Evermann (’96-00) give 
for Limanda 85 dorsal and 62 ventral fin-rays. The specimens of Li- 
manda I have counted at Wood’s Hole vary from 81 to 78 in the dorsal 
and 61 to 47 in the ventral. I counted the fin-rays in six small fishes, 
three of each type, and found that in two of these— they belonged to 
the 14 mm. type — the rays corresponded to the formula for Limanda, 
and that in one (9 mm. long) they agreed with P. americanus, there 
being 64 dorsal and 47 ventral rays. The number of rays in the other 
three were absolutely intermediate, two (8.5 mm. long) having respec- 
tively 71-54 and 76-51 rays, the remaining one 75-56 rays. 
The work of Kyle (98) at the St. Andrews laboratory is valuable for 
comparison at this point. There are five dextral flounders on the Scotch 
coast which may be confused with one another. The ones most like 
our species are Pleuronectes flesus, the flounder, P. platessa, the plaice, 
and P. limanda, the dab. Of these, when metamorphosis is completed, 
the flounder is the shortest (about 8 mm., according to Petersen), the 
plaice next and the dab the longest. The plaice may vary in length 
from 13 to 16 mm.; the dab from 16 to 19 mm. at metamorphosis. 
In Danish waters (Petersen, 94, p. 14) the metamorphoses of these two 
species are complete when the fish is from 4 to 6 mm. shorter. 
As the plaice and dab overlap each other in length, their fin formule 
were ascertained by Kyle in the hope of finding there a distinctive 
